Use Knuth Shuffle algo.
On Sun, Aug 15, 2010 at 8:34 PM, Rahul Singhal <nitk.ra...@gmail.com> wrote:
> Let X1, X2…. XN (In this case N=52) be the set of N numbers to be shuffled.
>
> 1. Set j to N
> 2. Generate a random number R. (uniformly distributed between 0 and 1)
> 3. Set k to (jR+1). k is now a random integer, between 1 and j.
> 4. Exchange Xk and Xj
> 5. Decrease j by 1.
> 6. If j > 1, return to step 2.
>
> void Shuffle(int* pArr)
> {
> int rand;
> for(int i=51;i>=0;i--)
> {
> rand=GenRand(0,i);
> swap(pArr[i], pArr[rand]);
> }
> }
>
> GenRand(int min, int max) generates a random number between min and max.
>
>
> On Sun, Aug 15, 2010 at 9:10 AM, Dave <dave_and_da...@juno.com> wrote:
>
>> @Sharad: Your code does not produce equally probable shuffles. You can
>> see this by noting that a[0] is swapped with one of 52 cards, same for
>> a[1], a[2], ..., a[51]. Thus, there are 52^52 possible sets of swaps.
>> But there are only 52! possible outcomes, and 52^52 / 52! is not an
>> integer.
>>
>> You can verify this experimentally by shuffling a small deck, say 3
>> cards. If you do so, you will find that, starting with the deck ABC,
>> you get ABC 4/27 of the time, ACB 5/27, BAC 5/27, BCA 5/27, CAB 4/27,
>> and CBA 4/27. Thus, some outcomes are 25% more likely than others.
>>
>> The proper code is
>> for(i=1;i<52;++i)
>> {
>> int r=rand()%(i+1);
>> swap(a[i],a[r]);
>> }
>>
>> Dave
>>
>> On Aug 14, 9:34 pm, sharad kumar <aryansmit3...@gmail.com> wrote:
>> > for(i=0;i<52;++i)
>> > {
>> > int r=rand()%52;
>> > swap(a[i],a[r]);
>> >
>> > }
>> > On Sat, Aug 14, 2010 at 11:46 PM, amit <amitjaspal...@gmail.com> wrote:
>> > > write a program to shuffle an pack of cards in the most efficient way.
>> >
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>
>
> --
> Rahul singhal
> RnD Engineer
> Tejas Networks
> Mobile- 09916969422
>
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