Count number of subsets whose median is also present in the same subset | JavaScript implementation of the approach ; Function to return the factorial of a number ; Function to return the value of nCr ; Function to return a raised to the power n with complexity O ( log ( n ) ) ; Function to return the number of sub - sets whose median is also present in the set ; Number of odd length sub - sets ; Sort the array ; Checking each element for leftmost middle element while they are equal ; Calculate the number of elements in right of rightmost middle element ; Calculate the number of elements in left of leftmost middle element ; Add selected even length subsets to the answer ; Driver code
const mod = 1000000007 ; function fact ( n ) { let res = 1 ; for ( let i = 2 ; i <= n ; i ++ ) res = res * i ; return res ; } function nCr ( n , r ) { return parseInt ( fact ( n ) / ( fact ( r ) * fact ( n - r ) ) ) ; } function powmod ( a , n ) { if ( ! n ) return 1 ; let pt = powmod ( a , parseInt ( n / 2 ) ) ; pt = ( pt * pt ) % mod ; if ( n % 2 ) return ( pt * a ) % mod ; else return pt ; } function CountSubset ( arr , n ) { let ans = powmod ( 2 , n - 1 ) ; arr . sort ( ) ; for ( let i = 0 ; i < n ; ++ i ) { let j = i + 1 ; while ( j < n && arr [ j ] == arr [ i ] ) { let r = n - 1 - j ; let l = i ; ans = ( ans + nCr ( l + r , l ) ) % mod ; j ++ ; } } return ans ; } let arr = [ 2 , 3 , 2 ] ; let n = arr . length ; document . write ( CountSubset ( arr , n ) ) ;