Count number of ways to partition a set into k subsets | Returns count of different partitions of n elements in k subsets ; Base cases ; S ( n + 1 , k ) = k * S ( n , k ) + S ( n , k - 1 ) ; Driver Code
< ? php function countP ( $ n , $ k ) { if ( $ n == 0 $ k == 0 $ k > $ n ) return 0 ; if ( $ k == 1 $ k == $ n ) return 1 ; return $ k * countP ( $ n - 1 , $ k ) + countP ( $ n - 1 , $ k - 1 ) ; } echo countP ( 3 , 2 ) ; ? >