Count of K length subsequence whose product is even | Function to calculate nCr ; Returns factorial of n ; Function for finding number of K length subsequences whose product is even number ; counting odd numbers in the array ; Driver code
function nCr ( n , r ) { if ( r > n ) return 0 ; return fact ( n ) / ( fact ( r ) * fact ( n - r ) ) ; } function fact ( n ) { var res = 1 ; for ( var i = 2 ; i <= n ; i ++ ) res = res * i ; return res ; } function countSubsequences ( arr , n , k ) { var countOdd = 0 ; for ( var i = 0 ; i < n ; i ++ ) { if ( arr [ i ] & 1 ) countOdd ++ ; } var ans = nCr ( n , k ) - nCr ( countOdd , k ) ; return ans ; } var arr = [ 2 , 4 ] ; var K = 1 ; var N = arr . length ; document . write ( countSubsequences ( arr , N , K ) ) ;