Number of ways in which an item returns back to its initial position in N swaps in array of size K | Javascript program to find the number of ways in which an item returns back to its initial position in N swaps in an array of size K ; Function to calculate ( x ^ y ) % p in O ( log y ) ; Initialize result ; Update x if it is more than or equal to p ; If y is odd , multiply x with result ; y must be even now y = y / 2 ; Function to return the number of ways ; Base case ; Recursive case F ( n ) = ( k - 1 ) ^ ( n - 1 ) - F ( n - 1 ) . ; Driver code ; Function calling
let mod = 1000000007 ; function power ( x , y ) { let p = mod ; let res = 1 ; x = x % p ; while ( y > 0 ) { if ( ( y & 1 ) > 0 ) res = ( res * x ) % p ; y = y >> 1 ; x = ( x * x ) % p ; } return res ; } function solve ( n , k ) { if ( n == 1 ) return 0 ; return ( power ( ( k - 1 ) , n - 1 ) % mod - solve ( n - 1 , k ) + mod ) % mod ; } let n = 4 , k = 5 ; document . write ( solve ( n , k ) ) ;