Find gcd ( a ^ n , c ) where a , n and c can vary from 1 to 10 ^ 9 | Iterative Function to calculate ( x ^ y ) % p in O ( log y ) ; x = x % p ; 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 >> 1 ; y = y / 2 ; Finds GCD of a and b ; Finds GCD of a ^ n and c ; check if c is a divisor of a ; First compute ( a ^ n ) % c ; Now simply return GCD of modulo power and c . ; Driver code
function modPower ( x , y , p ) { while ( y > 0 ) { if ( ( y & 1 ) > 0 ) res = ( res * x ) % p ; x = ( x * x ) % p ; } return res ; } function gcd ( a , b ) { if ( b == 0 ) return a ; return gcd ( b , a % b ) ; } function gcdPow ( a , n , c ) { if ( a % c == 0 ) return c ; let modexpo = modPower ( a , n , c ) ; return gcd ( modexpo , c ) ; } let a = 10248585 , n = 1000000 , c = 12564 ; document . write ( gcdPow ( a , n , c ) ) ;