Number of ways in which an item returns back to its initial position in N swaps in array of size K | Java 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
class GFG { static int mod = 1000000007 ; public static int power ( int x , int y ) { int p = mod ; int 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 ; } public static int solve ( int n , int k ) { if ( n == 1 ) return 0 ; return ( power ( ( k - 1 ) , n - 1 ) % mod - solve ( n - 1 , k ) + mod ) % mod ; } public static void main ( String [ ] args ) { int n = 4 , k = 5 ; System . out . println ( solve ( n , k ) ) ; } }