Re: [algogeeks] Virtual functions in constructor

2012-10-10 Thread atul anand
http://www.parashift.com/c++-faq/virtual-functions.html

On Wed, Oct 10, 2012 at 2:16 AM, rahul sharma rahul23111...@gmail.comwrote:

 Guys i have read that concept of virtual fxn is not applicable in case of
 constructors..I means using virtual function in constructors always call
 local function..i wan to read more on this..can nybody explain use of
 virtual functions in constructor or provide me with a link for this..

 thnx

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Re: [algogeeks] Min Edges to be added to DAG to make it Strongly connected?

2012-10-10 Thread KK
This is the 
linkhttp://apps.topcoder.com/forums/?module=ThreadthreadID=764182start=0mc=4#1614862to
 the answer given by misof.. and it worked!!

On Sunday, 7 October 2012 00:41:48 UTC+5:30, kailash wrote:

 @atul: No,it's not the correct answer. Let's take an example of star like 
 DAG:-

 A
 --B--C
   
   |
   
   V
   
  D
 This DAG contains only one cut vertex(B) but we need to add two edges to 
 make it strongly connected.
   
  


 On Sat, Oct 6, 2012 at 7:37 PM, atul anand atul.8...@gmail.comjavascript:
  wrote:

 find no. of cut vertex in the DAGthat will be the ans.
 On 6 Oct 2012 19:33, KK kunalka...@gmail.com javascript: wrote:

 Given a DAG(Directed Acyclic Graph). How to find out the minimum number 
 of edges that needs to be added so that the given graph becomes Strongly 
 Connected?

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 Computer Science  Engineering
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 Roorkee, India (247667)

 

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[algogeeks] Re: Help me find my Recursive algo complexity

2012-10-10 Thread KK
Hi Vicky.. Its O(n^K) as u are iterating over all the elements of array for 
each of the k element subset!!

On Monday, 8 October 2012 23:53:15 UTC+5:30, ((** VICKY **)) wrote:

 Hi, I wrote code for generating all possible sets of length k in a array 
 of length n. I did using recursion, but i'm not able to calc the 
 complexity systematically [image: :-/] Kindly help me.
  11:39 PM

 i.p {1,2,3,4,5} k =2
 o.p
 Vector has : 1 2 3 4 5  
 1 1 2 
 2 1 3 
 3 1 4 
 4 1 5 
 5 2 3 
 6 2 4 
 7 2 5 
 8 3 4 
 9 3 5 
 10 4 5 

 Approach:

 Assume I have a selected and remaining set, now initially all will be 
 remaining set and selected set= {}. 

 In first step pick 1 and grow recursion with it as root and pick 2,3,4,5 
 (n-1) as possible picks. Now print those sets since k=2(base case) is 
 reached. 
 Now grow recursion with 2 as root and 3,4,5 (n-2) as possible 
 picks(childs) print them. Repeat till i reach 5 where i have no children 
 possible as rem set is empty.   

 void print_all(vectorintsel,vectorintrem, int n){
 if(sel.size() == n)
 {
 static int cnt = 1;
 coutcnt++ ;
 for(int i = 0; i  n; i++)
 coutsel[i] ;
 coutendl;
 return;
 sel.erase(sel.begin(),sel.end());
 }
 for(int i = 0; i  rem.size(); i++)
 {
  
 vectorintnow,curr_sel;
 //for(int j = 0; j  i; j++)
   //  now.push_back(rem[j]);
 for(int j = i+1; jrem.size(); j++)
 now.push_back(rem[j]);
// coutnow has : ;
 //for(int i = 0; i  now.size(); i++)
   //  coutnow[i] ;
 //coutendl;
 for(int i = 0; i  sel.size(); i++)
 curr_sel.push_back(sel[i]);
 curr_sel.push_back(rem[i]);
 print_all(curr_sel,now,n);
 }}
  

 -- 
 Cheers,
  
   Vicky

  

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Re: [algogeeks] Virtual functions in constructor

2012-10-10 Thread Kumar Vishal
  FYI ..
 http://www.artima.com/cppsource/nevercall.html
 If you read the VTABLE and and how virtual function is implemented then
 you understand automatically why virtual is not applicable in constructor
 case .
 One more request its algo-group please try to avoid out of the topic
questions .
 Thanks
 Kumar Vishal



On Wed, Oct 10, 2012 at 2:16 AM, rahul sharma rahul23111...@gmail.comwrote:

 Guys i have read that concept of virtual fxn is not applicable in case of
 constructors..I means using virtual function in constructors always call
 local function..i wan to read more on this..can nybody explain use of
 virtual functions in constructor or provide me with a link for this..

 thnx

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Kumar Vishal
_
*http://wethecommonpeople.wordpress.com/   *
*h**ttp://kumartechnicalarticles.wordpress.com/http://kumartechnicalarticles.wordpress.com/
*
_

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Re: [algogeeks] this pointer help c++

2012-10-10 Thread Saurabh Kumar
 but i have read that reference is a const pointer
That is NOT true. A reference is not a const pointer. Period.
It's only because they 'point' to an object and cannot be changed to
'point' to some other object, people say its' a const pointer which is not
entirely true. References never 'point' to anything.
Reference is an *abstract concept*. an* alias *or a* 'different name for
same object'*.
A compiler may choose to implement it using a pointer or may not, it
depends on compiler.

 What is size of reference.
Had they been simple const pointers you'd get 4-Bytes(on 32 bit
architecture) or 8-Bytes (on 64 bit architectures). But what you'll
actually get is *size of the object* itself.
In fact ISO C++ standard itself says that whether or not a reference
requires a storage is unspecified. i.e. It is compiler dependent how they
are implemented internally.
But Internal implementation mechanisms will never alter the visible
behavior which is mandated by the Standard so, what sizeof(reference) will
return will always be size of Object itself.

what is return by reference??
It is nothing different than a reference initialization for all practical
purposes.

Let func be a function of class Circle:
*Circle Func(double r){*
* //Do something...*
* return *this;*
*}*
*
*
and, you call this function like: (This is how your *return by
reference*get's consumed.
*Circle ref = Func(7.5);* // { As we know reference initialization is done
with object and not by pointers to those objects so, *rvalue should be an
Object* of class Circle NOT a pointer.}

does it mean some pointer returned or it mean whole object returned??
The whole object is to be passed to the *'reference initialization'
mechanism* of the compiler. So you've to return an object itself(that's why
make sure you are returning some object that will persist after the
function call and not an object which will get destroyed with stack
unwinding of Func call.


Please don't say references are nothing but const pointers, just throw that
notion out of your head.
Points to gather:
*1. On the surface you can assume: References are just 'different names for
same object'. *
*2. While initializing them I need to pass the whole Object to the
reference initialization mechanism(which btw, is compiler dependent).*
*3. Sizeof(reference) is always the sizeof Object itself. (mandated by C++
standard)*
*4. Do references require extra storage? Maybe or maybe not. Read your
compiler docs.*

On 10 October 2012 02:30, rahul sharma rahul23111...@gmail.com wrote:

 Clear some more questiosn

 1. What is size of reference.

 2.what is return by reference???it means we return the object itself
 instead of copying it into temp. variable and then return as in c. in c++
 we return original variable itself..then when we return by reference wat
 does that mean,,,does it mean some pointer returned or it mean whole object
 returned??


 On Wed, Oct 10, 2012 at 2:23 AM, rahul sharma rahul23111...@gmail.comwrote:

 Got confusedcant get it..:([?]


 On Wed, Oct 10, 2012 at 1:00 AM, Prem Krishna Chettri hprem...@gmail.com
  wrote:

 Well Lemme try few more hand here..

 Basics First Guys :-

   this :-  is a hidden pointer to a class (Agree ?). So
 whats so special about it.. Answer is its compaction when the object of the
 class is being created. Why? Here it goes. As object memory allocation (I
 hope everyone knows) have memory structure such that the first parameter
 always starts with arg[1]. so why not arg[0] as array always indexes with
 0? The Answer is here.. Coz every time the object of a class is generated
 the Zeroth index is alwayz occupied by this *this* pointer. So if do
 you follow me up to here properly that you know the significance of this
 now.. Coz its object refference lies to the value of offset 0 to the base
 address of the class's object, giving the flexibility to express any member
 of the class by directly accessing via its base address and this also
 explains why this has to be a pointer and not a normal member variable.

Now here comes the other part of question.why we need *
 ** *this*  where *this* should give the base address of the object
 of the class we wanna refer. The Answer is partly YES coz as we discuss 
 *this *knows almost everything about the class or rather an object of
 a class within a class scope  but here is the catch we are telling someone
 to get a bowl of rice from my private house. So how will he be able to get
 it? Until I tell him my house structure, which in programming language like
 C++ is reference.

I am saying sir, I have created a house (object) and here is
 the layout (referring to what I have created) so inorder to tell him about
 my layout I have to generate the return value which is NOT the house
 (object) but the reference to the house ( pointer pointing to what I have
 created ).

  Now I am almost done here.. So Why   ** this * and not *this
 * is coz  *this*  gives the 

Re: [algogeeks] Virtual functions in constructor

2012-10-10 Thread Saurabh Kumar
In short: Call for virtual function in constructor is redirected to the
local function because, the derived part of the object has not being
initialized yet(remember you are still in Bases' constructor) and it makes
no sense to call a derived's implementation of a virtual function, which in
turn be using some (still uninitialized) non-static data members of derived
class.

You can read it in detail over here:
http://www.parashift.com/c%2B%2B-faq-lite/calling-virtuals-from-ctors.html

Also i recommend - *Inside the C++ Object Model* By Stanley B. Lippman.

Cheers,

On 10 October 2012 02:16, rahul sharma rahul23111...@gmail.com wrote:

 Guys i have read that concept of virtual fxn is not applicable in case of
 constructors..I means using virtual function in constructors always call
 local function..i wan to read more on this..can nybody explain use of
 virtual functions in constructor or provide me with a link for this..

 thnx

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Re: [algogeeks] Min Edges to be added to DAG to make it Strongly connected?

2012-10-10 Thread atul anand
i have doubts in miscof answer ,
your question says that given graph is a DAG ,but in miscof's reply he is
considering directed graph which contain say n strongly connected component
, so if we consider dat there are n strongly connected component in your
graph then that graph is not a DAG(this will violates your question).
But if you are considering all nodes in a given strongly connected graph as
a single node then given graph will form DAG.
so there is lot of difference in the twoso please clarify your
question.

On Wed, Oct 10, 2012 at 1:26 AM, KK kunalkapadi...@gmail.com wrote:

 This is the 
 linkhttp://apps.topcoder.com/forums/?module=ThreadthreadID=764182start=0mc=4#1614862to
  the answer given by misof.. and it worked!!


 On Sunday, 7 October 2012 00:41:48 UTC+5:30, kailash wrote:

 @atul: No,it's not the correct answer. Let's take an example of star like
 DAG:-

 A
 --B--C

   |

   V

  D
 This DAG contains only one cut vertex(B) but we need to add two edges to
 make it strongly connected.




 On Sat, Oct 6, 2012 at 7:37 PM, atul anand atul.8...@gmail.com wrote:

 find no. of cut vertex in the DAGthat will be the ans.
 On 6 Oct 2012 19:33, KK kunalka...@gmail.com wrote:

 Given a DAG(Directed Acyclic Graph). How to find out the minimum number
 of edges that needs to be added so that the given graph becomes Strongly
 Connected?

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 B-tech 4th year
 Computer Science  Engineering
 Indian Institute of Technology, Roorkee
 Roorkee, India (247667)

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[algogeeks] can we check a number has last digit 5 or not using bitwise operator.

2012-10-10 Thread mohit mishra


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Re: [algogeeks] rectangle of max sum MS Q

2012-10-10 Thread Priya Dhingra
@atul.ok i got it thanx a lot

On Tue, Oct 9, 2012 at 10:08 AM, atul anand atul.87fri...@gmail.com wrote:

 @priya : i dont knw , how you came up with these values ...!!! and
 aove code given is not a full code , it just a sketch of code to make
 you understand.Before moving further,i would like to clarify that
 innner K-loop is running kadane algo(full code is not written).
 so i cut short in this by discussing the idea behind it

 After finding cumulative sum of each column ..moving top to bottom ,
 Suppose we get this :-
 1 0 0 0
 1 1 1 -2
 1 2 2 -4
 2 3 2 -3

 now IDEA is start from last row. -- ( I-Loop is handling this )
 negate values i each cell of first row from the each cell for last row
 -- ( j-Loop is handling this )
 i.e
 2-1 , 3-0 , 2-0,  -3-0 == 1,3,2,-3
 1,3,2,-3 == now run kadane algo on this last row only and update max
 ( K-loop is doing this)

 similarly , when we increment j i.e now we move to second row which j
 loop is handling.
 do the same :-
 2-1,3-1, 2-1,-3-2 // --- run kadane algo on this and update max.

 now when j loop ends , then we are moving to second last row and doing
 the same ...as we did with last row in above example.

 i hope now you get it..

 On 10/9/12, Priya Dhingra priya.dhingr...@gmail.com wrote:
  i dnt know how ur algo is handling the case like [c2 d2 ,c3 d3] or [c1
 d1,
  c2 d2 ,c3 d3]
 
 
  as i run this loop it is considering the following matrices
 
 
 
 
 
  i=3 j=0 nd k=0 to 3
  [a2 a3 a4],[a2 b2,a3 b3,a4 b4].[a2 b2 c2,a3 b3 c3,a4 b4 c4],[a2 b2 c2 d2
  ,a3 b3 c3 d3,a4 b4 c4 d4]
 
  i=3 j=1 nd k=0 to 3
  [a3 a4], [a3 b3, a4 b4],[a3 b3 c3, a4 b4 c4 d4],[a3 b3 c3 d3 ,a4 b4 c4
 d4]
 
  i=3 j=2 k =0 to 3
  [a4] [a4 b4] [a4 b4 c4] [a4 b4 c4 d4]
 
  i=2 j=0 k=0 to 3
  [a2 a3] [a2 b2,a3 b3],[a2 b2 c2,a3 b3 c3],[a2 b2 c2 d2 ,a3 b3 c3 d3]
 
  i=2 j=1 k=0 to 3
  [a2] [a3 b3] [a3 b3 c3] [a3 b3 c3 d3]
 
  i=1 j= k =0 to 3
  [a2] [a2 b2] [a2 b2 c2][a2 b2 c2 d2]
 
 
 
  On Mon, Oct 8, 2012 at 9:53 PM, atul anand atul.87fri...@gmail.com
 wrote:
 
  @Priya : if first row is the max one , then it is actually boundary case
  which you can be handled easily,once you are done which above algo.
  please note that only first row need to checked if it max not every row
 ,
  above algo is handling this . you can also modify given algo which will
  handle this boundary case.
  for rest of the cases it will work fine. It is handling cases like...
  c2d2
  c3d3 etc...
  please try to understand idea behind the given algo ,let me know in case
  you have any further doubt.
 
 
  On Mon, Oct 8, 2012 at 10:52 PM, Priya Dhingra
  priya.dhingr...@gmail.comwrote:
 
  @atul  if the largest matrix is [a1  b1  c1  d1 ]  i mean if it is the
  first row or if it is [c2 d2.i think then then ur code wont be giving
  the
  right answer.
 c3 d3]
 
  correct me if i'm wrong
 
 
  On Monday, January 16, 2012 7:51:46 AM UTC-8, atul007 wrote:
 
 
  find cumulative sum of each column.
  now for each arr[x][y] = sum of arr[i=0 to x] [j] ;
 
  a1 b1 c1 d1
  a2 b2 c2 d2
  a3 b3 c3 d3
  a4 d4 c4 d4
 
  now we have reduced this problem to find max-subarray . which can
  be efficiently calculated using kadane's algo for each row.
 
  NOTE: now suppose if row = 0  does not participate in calculating max
  sum matrix so u need to subtract a1 from a2,a3,a4  similarly for
  other
  element in row 1,2,3.
 
  now updated matrix considered i.e from (row =1 to row =3 ). for this
  updated matrix,
   each[x][y] is the sum of arr[i=1 to x] [j].
 
  similarly do for other elements.
 
  On Mon, Jan 16, 2012 at 6:55 AM, Ashish Goel ash...@gmail.com
 wrote:
 
   given a m*n matrix, find the subset rectangle with max sum (any
 other
  rectangle taken would have lesser sum)
  Best Regards
  Ashish Goel
  Think positive and find fuel in failure
  +919985813081
  +919966006652
 
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Re: [algogeeks] this pointer help c++

2012-10-10 Thread rahul sharma
thnx a lot

On Wed, Oct 10, 2012 at 9:27 AM, Saurabh Kumar srbh.ku...@gmail.com wrote:

  but i have read that reference is a const pointer
 That is NOT true. A reference is not a const pointer. Period.
 It's only because they 'point' to an object and cannot be changed to
 'point' to some other object, people say its' a const pointer which is not
 entirely true. References never 'point' to anything.
 Reference is an *abstract concept*. an* alias *or a* 'different name for
 same object'*.
 A compiler may choose to implement it using a pointer or may not, it
 depends on compiler.

  What is size of reference.
 Had they been simple const pointers you'd get 4-Bytes(on 32 bit
 architecture) or 8-Bytes (on 64 bit architectures). But what you'll
 actually get is *size of the object* itself.
 In fact ISO C++ standard itself says that whether or not a reference
 requires a storage is unspecified. i.e. It is compiler dependent how they
 are implemented internally.
 But Internal implementation mechanisms will never alter the visible
 behavior which is mandated by the Standard so, what sizeof(reference) will
 return will always be size of Object itself.

 what is return by reference??
 It is nothing different than a reference initialization for all practical
 purposes.

 Let func be a function of class Circle:
 *Circle Func(double r){*
 * //Do something...*
 * return *this;*
 *}*
 *
 *
 and, you call this function like: (This is how your *return by 
 reference*get's consumed.
 *Circle ref = Func(7.5);* // { As we know reference initialization is
 done with object and not by pointers to those objects so, *rvalue should
 be an Object* of class Circle NOT a pointer.}

 does it mean some pointer returned or it mean whole object returned??
 The whole object is to be passed to the *'reference initialization'
 mechanism* of the compiler. So you've to return an object itself(that's
 why make sure you are returning some object that will persist after the
 function call and not an object which will get destroyed with stack
 unwinding of Func call.


 Please don't say references are nothing but const pointers, just throw
 that notion out of your head.
 Points to gather:
 *1. On the surface you can assume: References are just 'different names
 for same object'. *
 *2. While initializing them I need to pass the whole Object to the
 reference initialization mechanism(which btw, is compiler dependent).*
 *3. Sizeof(reference) is always the sizeof Object itself. (mandated by
 C++ standard)*
 *4. Do references require extra storage? Maybe or maybe not. Read your
 compiler docs.*

 On 10 October 2012 02:30, rahul sharma rahul23111...@gmail.com wrote:

 Clear some more questiosn

 1. What is size of reference.

 2.what is return by reference???it means we return the object itself
 instead of copying it into temp. variable and then return as in c. in c++
 we return original variable itself..then when we return by reference wat
 does that mean,,,does it mean some pointer returned or it mean whole object
 returned??


 On Wed, Oct 10, 2012 at 2:23 AM, rahul sharma rahul23111...@gmail.comwrote:

 Got confusedcant get it..:([?]


 On Wed, Oct 10, 2012 at 1:00 AM, Prem Krishna Chettri 
 hprem...@gmail.com wrote:

 Well Lemme try few more hand here..

 Basics First Guys :-

   this :-  is a hidden pointer to a class (Agree ?). So
 whats so special about it.. Answer is its compaction when the object of the
 class is being created. Why? Here it goes. As object memory allocation (I
 hope everyone knows) have memory structure such that the first parameter
 always starts with arg[1]. so why not arg[0] as array always indexes with
 0? The Answer is here.. Coz every time the object of a class is generated
 the Zeroth index is alwayz occupied by this *this* pointer. So if do
 you follow me up to here properly that you know the significance of this
 now.. Coz its object refference lies to the value of offset 0 to the base
 address of the class's object, giving the flexibility to express any member
 of the class by directly accessing via its base address and this also
 explains why this has to be a pointer and not a normal member variable.

Now here comes the other part of question.why we need *
  ** *this*  where *this* should give the base address of the
 object of the class we wanna refer. The Answer is partly YES coz as we
 discuss *this *knows almost everything about the class or rather an
 object of a class within a class scope  but here is the catch we are
 telling someone to get a bowl of rice from my private house. So how will he
 be able to get it? Until I tell him my house structure, which in
 programming language like C++ is reference.

I am saying sir, I have created a house (object) and here is
 the layout (referring to what I have created) so inorder to tell him about
 my layout I have to generate the return value which is NOT the house
 (object) but the reference to the house ( pointer 

Re: [algogeeks] Virtual functions in constructor

2012-10-10 Thread rahul sharma
@vishal...i know its algo group..i was not getting exact answer..so
posted...hope it will also help someone.

On Wed, Oct 10, 2012 at 9:53 AM, Saurabh Kumar srbh.ku...@gmail.com wrote:

 In short: Call for virtual function in constructor is redirected to the
 local function because, the derived part of the object has not being
 initialized yet(remember you are still in Bases' constructor) and it makes
 no sense to call a derived's implementation of a virtual function, which in
 turn be using some (still uninitialized) non-static data members of derived
 class.

 You can read it in detail over here:
 http://www.parashift.com/c%2B%2B-faq-lite/calling-virtuals-from-ctors.html

 Also i recommend - *Inside the C++ Object Model* By Stanley B. Lippman.

 Cheers,

 On 10 October 2012 02:16, rahul sharma rahul23111...@gmail.com wrote:

 Guys i have read that concept of virtual fxn is not applicable in case of
 constructors..I means using virtual function in constructors always call
 local function..i wan to read more on this..can nybody explain use of
 virtual functions in constructor or provide me with a link for this..

 thnx

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[algogeeks] Re: can we check a number has last digit 5 or not using bitwise operator.

2012-10-10 Thread Dave
@Mohit: The decimal representation of a number ends in 5 if its low order 
bit is 1 and it is divisibile by 5. 
 
An algorithm using bitwise operations to check for divisibility by 5 is 
given at https://groups.google.com/d/msg/algogeeks/I5HWmwKW_ks/n38FWJSd0l8J.  

 
It probably is not as fast as (n  1)  (n % 5 == 0), though.
 
Dave

On Wednesday, October 10, 2012 4:06:28 AM UTC-5, mohit mishra wrote:




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