http://en.wikipedia.org/wiki/Catalan_number
On Sun, Oct 21, 2012 at 4:00 PM, Shruti Gupta wrote:
> if n=1,2,3 n we denote Push by "P" and Pop by "X"
> the we can generate following permutations :
>
> 1) PPPXXX = 321
> 2) PPXXPX = 213
> 3) PXPXPX = 123
> 4) PXPPXX = 132
> 5) PPXPXX = 231
>
> condi
if n=1,2,3 n we denote Push by "P" and Pop by "X"
the we can generate following permutations :
1) PPPXXX = 321
2) PPXXPX = 213
3) PXPXPX = 123
4) PXPPXX = 132
5) PPXPXX = 231
conditions : #P's = #X's and At no point, #X's>#P's
Ques :- Given n elements, find the number of permutations which are
