Count of binary strings of length N having equal count of 0 ' s ▁ and ▁ 1' s and count of 1 ' s ▁ â ‰ ¥ ▁ count ▁ of ▁ 0' s in each prefix substring | Java program to implement the above approach ; Function to calculate and returns the value of Binomial Coefficient C ( n , k ) ; Since C ( n , k ) = C ( n , n - k ) ; Calculate the value of [ n * ( n - 1 ) * -- - * ( n - k + 1 ) ] / [ k * ( k - 1 ) * -- - * 1 ] ; Function to return the count of all binary strings having equal count of 0 ' s ▁ and ▁ 1' s and each prefix substring having frequency of 1 ' s ▁ > = ▁ frequencies ▁ of ▁ 0' s ; If N is odd ; No such strings possible ; Otherwise ; Calculate value of 2 nCn ; Return 2 nCn / ( n + 1 ) ; Driver code
import java . util . * ; class GFG { static long binomialCoeff ( int n , int k ) { long res = 1 ; if ( k > n - k ) k = n - k ; for ( int i = 0 ; i < k ; ++ i ) { res *= ( n - i ) ; res /= ( i + 1 ) ; } return res ; } static long countStrings ( int N ) { if ( N % 2 == 1 ) return 0 ; else { N /= 2 ; long c = binomialCoeff ( 2 * N , N ) ; return c / ( N + 1 ) ; } } public static void main ( String [ ] args ) { int N = 6 ; System . out . print ( countStrings ( N ) + " ▁ " ) ; } }