Re: [algogeeks] Re: Implement a queue using a stack
if two stacks then possible otherwise i dont think so On Mon, Apr 12, 2010 at 11:39 PM, Dheeraj Jain dheerajj...@gmail.comwrote: Here is code and explanation http://geeksforgeeks.org/?p=5009 On Sat, Apr 10, 2010 at 10:18 PM, Rohit Saraf rohit.kumar.sa...@gmail.com wrote: hmm... that can always be done ! -- Rohit Saraf Second Year Undergraduate, Dept. of Computer Science and Engineering IIT Bombay http://www.cse.iitb.ac.in/~rohitfeb14http://www.cse.iitb.ac.in/%7Erohitfeb14 On Wed, Mar 24, 2010 at 6:24 PM, Dave dave_and_da...@juno.com wrote: Please post your results. I'd like to study your algorithm. On Mar 23, 11:15 pm, chitta koushik koushik.infin...@gmail.com wrote: yeah i understand that . still wanted to attempt writing a recursive reverse() stack operation. On Wed, Mar 24, 2010 at 9:21 AM, Rohit Saraf rohit.kumar.sa...@gmail.comwrote: Even when you are writing a recursive function.. you are not using one stack. One stack is yours. Other used for recursion. Making queue from a single stack = Making turing machine from CFG. -Rohit On Wed, Mar 24, 2010 at 9:18 AM, chitta koushik koushik.infin...@gmail.com wrote: Can we implement it using a single stack by writing a recursive reverse stack operation ? On Tue, Mar 23, 2010 at 10:18 AM, Sundeep Singh singh.sund...@gmail.comwrote: Thanks Dave, I didn't think about this... definitely better! Sundeep. On Mon, Mar 22, 2010 at 9:08 PM, Dave dave_and_da...@juno.com wrote: Better still. To enqueue: push onto stack A. For dequeuing: If stack B is empty, pop all items from stack A and push onto stack B. Then pop stack B. There is no need to push remaining items back to stack A. As every item passes through the queue, it is pushed onto stack A, then popped from stack A and pushed onto stack B, and finally popped from stack B. The time is roughly twice the time required for a direct implementation of a queue. There is room for a little optimization if both stacks are empty when enquing, as you can push the item directly onto stack B. Furthermore, when popping from stack A and pushing onto stack B, you don't need to push the last item popped, as it is the return value. Dave On Mar 22, 9:29 am, Sundeep Singh singh.sund...@gmail.com wrote: Hey Brian, Better still, for inserting in queue, just keep pushing onto the stack A. You need stack B only for dequeuing: for dequeuing, push all items into stack B, pop as many as you want from stack B and then push back all remaining items in stack A. Regards, Sundeep. On Mon, Mar 22, 2010 at 6:56 PM, Brian brianfo...@gmail.com wrote: How is it possible to implement a queue using a stack only? Interesting, but tricky... You need two stacks as Prakhar stated... In general, if you have Stack A and Stack B, you should keep all the items in stack A and then use stack B for processing. For example to insert an item: 1. Pop all the items from A and then push them into B (this should push the items into Stack B in reverse order) 2. Insert the new item into A 3. Pop all the items in B and push them back into A (again this will push them back into Stack B in reverse order) Running time should be O(1)+O(2n), which is O(n) for larger values of n - which is not good... To retrieve an item, pop the first item in stack A Hope this helps - Regards B On 3/22/2010 4:55 AM, Prakhar Jain wrote: By a do u mean a single stack ? Otherwise if you use 2 its v simple Best, Prakhar Jain http://web.iiit.ac.in/~prakharjain/http://web.iiit.ac.in/%7Eprakharjain/ http://web.iiit.ac.in/%7Eprakharjain/ http://web.iiit.ac.in/%7Eprakharjain/ On Mon, Mar 22, 2010 at 12:56 AM, Pushpesh Gupta pushpes...@gmail.comwrote: How is it possible to implement a queue using a stack only? -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com
Re: [algogeeks] Re: Implement a queue using a stack
Here is code and explanation http://geeksforgeeks.org/?p=5009 On Sat, Apr 10, 2010 at 10:18 PM, Rohit Saraf rohit.kumar.sa...@gmail.comwrote: hmm... that can always be done ! -- Rohit Saraf Second Year Undergraduate, Dept. of Computer Science and Engineering IIT Bombay http://www.cse.iitb.ac.in/~rohitfeb14http://www.cse.iitb.ac.in/%7Erohitfeb14 On Wed, Mar 24, 2010 at 6:24 PM, Dave dave_and_da...@juno.com wrote: Please post your results. I'd like to study your algorithm. On Mar 23, 11:15 pm, chitta koushik koushik.infin...@gmail.com wrote: yeah i understand that . still wanted to attempt writing a recursive reverse() stack operation. On Wed, Mar 24, 2010 at 9:21 AM, Rohit Saraf rohit.kumar.sa...@gmail.comwrote: Even when you are writing a recursive function.. you are not using one stack. One stack is yours. Other used for recursion. Making queue from a single stack = Making turing machine from CFG. -Rohit On Wed, Mar 24, 2010 at 9:18 AM, chitta koushik koushik.infin...@gmail.com wrote: Can we implement it using a single stack by writing a recursive reverse stack operation ? On Tue, Mar 23, 2010 at 10:18 AM, Sundeep Singh singh.sund...@gmail.comwrote: Thanks Dave, I didn't think about this... definitely better! Sundeep. On Mon, Mar 22, 2010 at 9:08 PM, Dave dave_and_da...@juno.com wrote: Better still. To enqueue: push onto stack A. For dequeuing: If stack B is empty, pop all items from stack A and push onto stack B. Then pop stack B. There is no need to push remaining items back to stack A. As every item passes through the queue, it is pushed onto stack A, then popped from stack A and pushed onto stack B, and finally popped from stack B. The time is roughly twice the time required for a direct implementation of a queue. There is room for a little optimization if both stacks are empty when enquing, as you can push the item directly onto stack B. Furthermore, when popping from stack A and pushing onto stack B, you don't need to push the last item popped, as it is the return value. Dave On Mar 22, 9:29 am, Sundeep Singh singh.sund...@gmail.com wrote: Hey Brian, Better still, for inserting in queue, just keep pushing onto the stack A. You need stack B only for dequeuing: for dequeuing, push all items into stack B, pop as many as you want from stack B and then push back all remaining items in stack A. Regards, Sundeep. On Mon, Mar 22, 2010 at 6:56 PM, Brian brianfo...@gmail.com wrote: How is it possible to implement a queue using a stack only? Interesting, but tricky... You need two stacks as Prakhar stated... In general, if you have Stack A and Stack B, you should keep all the items in stack A and then use stack B for processing. For example to insert an item: 1. Pop all the items from A and then push them into B (this should push the items into Stack B in reverse order) 2. Insert the new item into A 3. Pop all the items in B and push them back into A (again this will push them back into Stack B in reverse order) Running time should be O(1)+O(2n), which is O(n) for larger values of n - which is not good... To retrieve an item, pop the first item in stack A Hope this helps - Regards B On 3/22/2010 4:55 AM, Prakhar Jain wrote: By a do u mean a single stack ? Otherwise if you use 2 its v simple Best, Prakhar Jain http://web.iiit.ac.in/~prakharjain/http://web.iiit.ac.in/%7Eprakharjain/ http://web.iiit.ac.in/%7Eprakharjain/ http://web.iiit.ac.in/%7Eprakharjain/ On Mon, Mar 22, 2010 at 12:56 AM, Pushpesh Gupta pushpes...@gmail.comwrote: How is it possible to implement a queue using a stack only? -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this
Re: [algogeeks] Re: Implement a queue using a stack
hmm... that can always be done ! -- Rohit Saraf Second Year Undergraduate, Dept. of Computer Science and Engineering IIT Bombay http://www.cse.iitb.ac.in/~rohitfeb14 On Wed, Mar 24, 2010 at 6:24 PM, Dave dave_and_da...@juno.com wrote: Please post your results. I'd like to study your algorithm. On Mar 23, 11:15 pm, chitta koushik koushik.infin...@gmail.com wrote: yeah i understand that . still wanted to attempt writing a recursive reverse() stack operation. On Wed, Mar 24, 2010 at 9:21 AM, Rohit Saraf rohit.kumar.sa...@gmail.comwrote: Even when you are writing a recursive function.. you are not using one stack. One stack is yours. Other used for recursion. Making queue from a single stack = Making turing machine from CFG. -Rohit On Wed, Mar 24, 2010 at 9:18 AM, chitta koushik koushik.infin...@gmail.com wrote: Can we implement it using a single stack by writing a recursive reverse stack operation ? On Tue, Mar 23, 2010 at 10:18 AM, Sundeep Singh singh.sund...@gmail.comwrote: Thanks Dave, I didn't think about this... definitely better! Sundeep. On Mon, Mar 22, 2010 at 9:08 PM, Dave dave_and_da...@juno.com wrote: Better still. To enqueue: push onto stack A. For dequeuing: If stack B is empty, pop all items from stack A and push onto stack B. Then pop stack B. There is no need to push remaining items back to stack A. As every item passes through the queue, it is pushed onto stack A, then popped from stack A and pushed onto stack B, and finally popped from stack B. The time is roughly twice the time required for a direct implementation of a queue. There is room for a little optimization if both stacks are empty when enquing, as you can push the item directly onto stack B. Furthermore, when popping from stack A and pushing onto stack B, you don't need to push the last item popped, as it is the return value. Dave On Mar 22, 9:29 am, Sundeep Singh singh.sund...@gmail.com wrote: Hey Brian, Better still, for inserting in queue, just keep pushing onto the stack A. You need stack B only for dequeuing: for dequeuing, push all items into stack B, pop as many as you want from stack B and then push back all remaining items in stack A. Regards, Sundeep. On Mon, Mar 22, 2010 at 6:56 PM, Brian brianfo...@gmail.com wrote: How is it possible to implement a queue using a stack only? Interesting, but tricky... You need two stacks as Prakhar stated... In general, if you have Stack A and Stack B, you should keep all the items in stack A and then use stack B for processing. For example to insert an item: 1. Pop all the items from A and then push them into B (this should push the items into Stack B in reverse order) 2. Insert the new item into A 3. Pop all the items in B and push them back into A (again this will push them back into Stack B in reverse order) Running time should be O(1)+O(2n), which is O(n) for larger values of n - which is not good... To retrieve an item, pop the first item in stack A Hope this helps - Regards B On 3/22/2010 4:55 AM, Prakhar Jain wrote: By a do u mean a single stack ? Otherwise if you use 2 its v simple Best, Prakhar Jain http://web.iiit.ac.in/~prakharjain/ http://web.iiit.ac.in/%7Eprakharjain/ http://web.iiit.ac.in/%7Eprakharjain/ On Mon, Mar 22, 2010 at 12:56 AM, Pushpesh Gupta pushpes...@gmail.comwrote: How is it possible to implement a queue using a stack only? -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algogeeks@googlegroups.com . To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algogeeks@googlegroups.com . To unsubscribe from this group, send email to
[algogeeks] Re: Implement a queue using a stack
Please post your results. I'd like to study your algorithm. On Mar 23, 11:15 pm, chitta koushik koushik.infin...@gmail.com wrote: yeah i understand that . still wanted to attempt writing a recursive reverse() stack operation. On Wed, Mar 24, 2010 at 9:21 AM, Rohit Saraf rohit.kumar.sa...@gmail.comwrote: Even when you are writing a recursive function.. you are not using one stack. One stack is yours. Other used for recursion. Making queue from a single stack = Making turing machine from CFG. -Rohit On Wed, Mar 24, 2010 at 9:18 AM, chitta koushik koushik.infin...@gmail.com wrote: Can we implement it using a single stack by writing a recursive reverse stack operation ? On Tue, Mar 23, 2010 at 10:18 AM, Sundeep Singh singh.sund...@gmail.comwrote: Thanks Dave, I didn't think about this... definitely better! Sundeep. On Mon, Mar 22, 2010 at 9:08 PM, Dave dave_and_da...@juno.com wrote: Better still. To enqueue: push onto stack A. For dequeuing: If stack B is empty, pop all items from stack A and push onto stack B. Then pop stack B. There is no need to push remaining items back to stack A. As every item passes through the queue, it is pushed onto stack A, then popped from stack A and pushed onto stack B, and finally popped from stack B. The time is roughly twice the time required for a direct implementation of a queue. There is room for a little optimization if both stacks are empty when enquing, as you can push the item directly onto stack B. Furthermore, when popping from stack A and pushing onto stack B, you don't need to push the last item popped, as it is the return value. Dave On Mar 22, 9:29 am, Sundeep Singh singh.sund...@gmail.com wrote: Hey Brian, Better still, for inserting in queue, just keep pushing onto the stack A. You need stack B only for dequeuing: for dequeuing, push all items into stack B, pop as many as you want from stack B and then push back all remaining items in stack A. Regards, Sundeep. On Mon, Mar 22, 2010 at 6:56 PM, Brian brianfo...@gmail.com wrote: How is it possible to implement a queue using a stack only? Interesting, but tricky... You need two stacks as Prakhar stated... In general, if you have Stack A and Stack B, you should keep all the items in stack A and then use stack B for processing. For example to insert an item: 1. Pop all the items from A and then push them into B (this should push the items into Stack B in reverse order) 2. Insert the new item into A 3. Pop all the items in B and push them back into A (again this will push them back into Stack B in reverse order) Running time should be O(1)+O(2n), which is O(n) for larger values of n - which is not good... To retrieve an item, pop the first item in stack A Hope this helps - Regards B On 3/22/2010 4:55 AM, Prakhar Jain wrote: By a do u mean a single stack ? Otherwise if you use 2 its v simple Best, Prakhar Jain http://web.iiit.ac.in/~prakharjain/http://web.iiit.ac.in/%7Eprakharjain/ http://web.iiit.ac.in/%7Eprakharjain/ On Mon, Mar 22, 2010 at 12:56 AM, Pushpesh Gupta pushpes...@gmail.comwrote: How is it possible to implement a queue using a stack only? -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.-Hide quoted text - - Show quoted text - -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to
Re: [algogeeks] Re: Implement a queue using a stack
Thanks Dave, I didn't think about this... definitely better! Sundeep. On Mon, Mar 22, 2010 at 9:08 PM, Dave dave_and_da...@juno.com wrote: Better still. To enqueue: push onto stack A. For dequeuing: If stack B is empty, pop all items from stack A and push onto stack B. Then pop stack B. There is no need to push remaining items back to stack A. As every item passes through the queue, it is pushed onto stack A, then popped from stack A and pushed onto stack B, and finally popped from stack B. The time is roughly twice the time required for a direct implementation of a queue. There is room for a little optimization if both stacks are empty when enquing, as you can push the item directly onto stack B. Furthermore, when popping from stack A and pushing onto stack B, you don't need to push the last item popped, as it is the return value. Dave On Mar 22, 9:29 am, Sundeep Singh singh.sund...@gmail.com wrote: Hey Brian, Better still, for inserting in queue, just keep pushing onto the stack A. You need stack B only for dequeuing: for dequeuing, push all items into stack B, pop as many as you want from stack B and then push back all remaining items in stack A. Regards, Sundeep. On Mon, Mar 22, 2010 at 6:56 PM, Brian brianfo...@gmail.com wrote: How is it possible to implement a queue using a stack only? Interesting, but tricky... You need two stacks as Prakhar stated... In general, if you have Stack A and Stack B, you should keep all the items in stack A and then use stack B for processing. For example to insert an item: 1. Pop all the items from A and then push them into B (this should push the items into Stack B in reverse order) 2. Insert the new item into A 3. Pop all the items in B and push them back into A (again this will push them back into Stack B in reverse order) Running time should be O(1)+O(2n), which is O(n) for larger values of n - which is not good... To retrieve an item, pop the first item in stack A Hope this helps - Regards B On 3/22/2010 4:55 AM, Prakhar Jain wrote: By a do u mean a single stack ? Otherwise if you use 2 its v simple Best, Prakhar Jain http://web.iiit.ac.in/~prakharjain/http://web.iiit.ac.in/%7Eprakharjain/ http://web.iiit.ac.in/%7Eprakharjain/ On Mon, Mar 22, 2010 at 12:56 AM, Pushpesh Gupta pushpes...@gmail.com wrote: How is it possible to implement a queue using a stack only? -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.- Hide quoted text - - Show quoted text - -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.
Re: [algogeeks] Re: Implement a queue using a stack
Can we implement it using a single stack by writing a recursive reverse stack operation ? On Tue, Mar 23, 2010 at 10:18 AM, Sundeep Singh singh.sund...@gmail.comwrote: Thanks Dave, I didn't think about this... definitely better! Sundeep. On Mon, Mar 22, 2010 at 9:08 PM, Dave dave_and_da...@juno.com wrote: Better still. To enqueue: push onto stack A. For dequeuing: If stack B is empty, pop all items from stack A and push onto stack B. Then pop stack B. There is no need to push remaining items back to stack A. As every item passes through the queue, it is pushed onto stack A, then popped from stack A and pushed onto stack B, and finally popped from stack B. The time is roughly twice the time required for a direct implementation of a queue. There is room for a little optimization if both stacks are empty when enquing, as you can push the item directly onto stack B. Furthermore, when popping from stack A and pushing onto stack B, you don't need to push the last item popped, as it is the return value. Dave On Mar 22, 9:29 am, Sundeep Singh singh.sund...@gmail.com wrote: Hey Brian, Better still, for inserting in queue, just keep pushing onto the stack A. You need stack B only for dequeuing: for dequeuing, push all items into stack B, pop as many as you want from stack B and then push back all remaining items in stack A. Regards, Sundeep. On Mon, Mar 22, 2010 at 6:56 PM, Brian brianfo...@gmail.com wrote: How is it possible to implement a queue using a stack only? Interesting, but tricky... You need two stacks as Prakhar stated... In general, if you have Stack A and Stack B, you should keep all the items in stack A and then use stack B for processing. For example to insert an item: 1. Pop all the items from A and then push them into B (this should push the items into Stack B in reverse order) 2. Insert the new item into A 3. Pop all the items in B and push them back into A (again this will push them back into Stack B in reverse order) Running time should be O(1)+O(2n), which is O(n) for larger values of n - which is not good... To retrieve an item, pop the first item in stack A Hope this helps - Regards B On 3/22/2010 4:55 AM, Prakhar Jain wrote: By a do u mean a single stack ? Otherwise if you use 2 its v simple Best, Prakhar Jain http://web.iiit.ac.in/~prakharjain/http://web.iiit.ac.in/%7Eprakharjain/ http://web.iiit.ac.in/%7Eprakharjain/ On Mon, Mar 22, 2010 at 12:56 AM, Pushpesh Gupta pushpes...@gmail.comwrote: How is it possible to implement a queue using a stack only? -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.- Hide quoted text - - Show quoted text - -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this
Re: [algogeeks] Re: Implement a queue using a stack
Even when you are writing a recursive function.. you are not using one stack. One stack is yours. Other used for recursion. Making queue from a single stack = Making turing machine from CFG. -Rohit On Wed, Mar 24, 2010 at 9:18 AM, chitta koushik koushik.infin...@gmail.comwrote: Can we implement it using a single stack by writing a recursive reverse stack operation ? On Tue, Mar 23, 2010 at 10:18 AM, Sundeep Singh singh.sund...@gmail.comwrote: Thanks Dave, I didn't think about this... definitely better! Sundeep. On Mon, Mar 22, 2010 at 9:08 PM, Dave dave_and_da...@juno.com wrote: Better still. To enqueue: push onto stack A. For dequeuing: If stack B is empty, pop all items from stack A and push onto stack B. Then pop stack B. There is no need to push remaining items back to stack A. As every item passes through the queue, it is pushed onto stack A, then popped from stack A and pushed onto stack B, and finally popped from stack B. The time is roughly twice the time required for a direct implementation of a queue. There is room for a little optimization if both stacks are empty when enquing, as you can push the item directly onto stack B. Furthermore, when popping from stack A and pushing onto stack B, you don't need to push the last item popped, as it is the return value. Dave On Mar 22, 9:29 am, Sundeep Singh singh.sund...@gmail.com wrote: Hey Brian, Better still, for inserting in queue, just keep pushing onto the stack A. You need stack B only for dequeuing: for dequeuing, push all items into stack B, pop as many as you want from stack B and then push back all remaining items in stack A. Regards, Sundeep. On Mon, Mar 22, 2010 at 6:56 PM, Brian brianfo...@gmail.com wrote: How is it possible to implement a queue using a stack only? Interesting, but tricky... You need two stacks as Prakhar stated... In general, if you have Stack A and Stack B, you should keep all the items in stack A and then use stack B for processing. For example to insert an item: 1. Pop all the items from A and then push them into B (this should push the items into Stack B in reverse order) 2. Insert the new item into A 3. Pop all the items in B and push them back into A (again this will push them back into Stack B in reverse order) Running time should be O(1)+O(2n), which is O(n) for larger values of n - which is not good... To retrieve an item, pop the first item in stack A Hope this helps - Regards B On 3/22/2010 4:55 AM, Prakhar Jain wrote: By a do u mean a single stack ? Otherwise if you use 2 its v simple Best, Prakhar Jain http://web.iiit.ac.in/~prakharjain/http://web.iiit.ac.in/%7Eprakharjain/ http://web.iiit.ac.in/%7Eprakharjain/ On Mon, Mar 22, 2010 at 12:56 AM, Pushpesh Gupta pushpes...@gmail.comwrote: How is it possible to implement a queue using a stack only? -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.- Hide quoted text - - Show quoted text - -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com
Re: [algogeeks] Re: Implement a queue using a stack
yeah i understand that . still wanted to attempt writing a recursive reverse() stack operation. On Wed, Mar 24, 2010 at 9:21 AM, Rohit Saraf rohit.kumar.sa...@gmail.comwrote: Even when you are writing a recursive function.. you are not using one stack. One stack is yours. Other used for recursion. Making queue from a single stack = Making turing machine from CFG. -Rohit On Wed, Mar 24, 2010 at 9:18 AM, chitta koushik koushik.infin...@gmail.com wrote: Can we implement it using a single stack by writing a recursive reverse stack operation ? On Tue, Mar 23, 2010 at 10:18 AM, Sundeep Singh singh.sund...@gmail.comwrote: Thanks Dave, I didn't think about this... definitely better! Sundeep. On Mon, Mar 22, 2010 at 9:08 PM, Dave dave_and_da...@juno.com wrote: Better still. To enqueue: push onto stack A. For dequeuing: If stack B is empty, pop all items from stack A and push onto stack B. Then pop stack B. There is no need to push remaining items back to stack A. As every item passes through the queue, it is pushed onto stack A, then popped from stack A and pushed onto stack B, and finally popped from stack B. The time is roughly twice the time required for a direct implementation of a queue. There is room for a little optimization if both stacks are empty when enquing, as you can push the item directly onto stack B. Furthermore, when popping from stack A and pushing onto stack B, you don't need to push the last item popped, as it is the return value. Dave On Mar 22, 9:29 am, Sundeep Singh singh.sund...@gmail.com wrote: Hey Brian, Better still, for inserting in queue, just keep pushing onto the stack A. You need stack B only for dequeuing: for dequeuing, push all items into stack B, pop as many as you want from stack B and then push back all remaining items in stack A. Regards, Sundeep. On Mon, Mar 22, 2010 at 6:56 PM, Brian brianfo...@gmail.com wrote: How is it possible to implement a queue using a stack only? Interesting, but tricky... You need two stacks as Prakhar stated... In general, if you have Stack A and Stack B, you should keep all the items in stack A and then use stack B for processing. For example to insert an item: 1. Pop all the items from A and then push them into B (this should push the items into Stack B in reverse order) 2. Insert the new item into A 3. Pop all the items in B and push them back into A (again this will push them back into Stack B in reverse order) Running time should be O(1)+O(2n), which is O(n) for larger values of n - which is not good... To retrieve an item, pop the first item in stack A Hope this helps - Regards B On 3/22/2010 4:55 AM, Prakhar Jain wrote: By a do u mean a single stack ? Otherwise if you use 2 its v simple Best, Prakhar Jain http://web.iiit.ac.in/~prakharjain/http://web.iiit.ac.in/%7Eprakharjain/ http://web.iiit.ac.in/%7Eprakharjain/ On Mon, Mar 22, 2010 at 12:56 AM, Pushpesh Gupta pushpes...@gmail.comwrote: How is it possible to implement a queue using a stack only? -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com algogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.- Hide quoted text - - Show quoted text - -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group.
[algogeeks] Re: Implement a queue using a stack
Better still. To enqueue: push onto stack A. For dequeuing: If stack B is empty, pop all items from stack A and push onto stack B. Then pop stack B. There is no need to push remaining items back to stack A. As every item passes through the queue, it is pushed onto stack A, then popped from stack A and pushed onto stack B, and finally popped from stack B. The time is roughly twice the time required for a direct implementation of a queue. There is room for a little optimization if both stacks are empty when enquing, as you can push the item directly onto stack B. Furthermore, when popping from stack A and pushing onto stack B, you don't need to push the last item popped, as it is the return value. Dave On Mar 22, 9:29 am, Sundeep Singh singh.sund...@gmail.com wrote: Hey Brian, Better still, for inserting in queue, just keep pushing onto the stack A. You need stack B only for dequeuing: for dequeuing, push all items into stack B, pop as many as you want from stack B and then push back all remaining items in stack A. Regards, Sundeep. On Mon, Mar 22, 2010 at 6:56 PM, Brian brianfo...@gmail.com wrote: How is it possible to implement a queue using a stack only? Interesting, but tricky... You need two stacks as Prakhar stated... In general, if you have Stack A and Stack B, you should keep all the items in stack A and then use stack B for processing. For example to insert an item: 1. Pop all the items from A and then push them into B (this should push the items into Stack B in reverse order) 2. Insert the new item into A 3. Pop all the items in B and push them back into A (again this will push them back into Stack B in reverse order) Running time should be O(1)+O(2n), which is O(n) for larger values of n - which is not good... To retrieve an item, pop the first item in stack A Hope this helps - Regards B On 3/22/2010 4:55 AM, Prakhar Jain wrote: By a do u mean a single stack ? Otherwise if you use 2 its v simple Best, Prakhar Jain http://web.iiit.ac.in/~prakharjain/http://web.iiit.ac.in/%7Eprakharjain/ On Mon, Mar 22, 2010 at 12:56 AM, Pushpesh Gupta pushpes...@gmail.comwrote: How is it possible to implement a queue using a stack only? -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.- Hide quoted text - - Show quoted text - -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.
