Sum of Digits in a ^ n till a single digit | Java program to find single digit sum of a ^ n . ; This function finds single digit sum of n . ; Returns single digit sum of a ^ n . We use modular exponentiation technique . ; Driver code
import java . util . * ; import java . lang . * ; import java . io . * ; class GFG { static int digSum ( int n ) { if ( n == 0 ) return 0 ; return ( n % 9 == 0 ) ? 9 : ( n % 9 ) ; } static int powerDigitSum ( int a , int n ) { int res = 1 ; while ( n > 0 ) { if ( n % 2 == 1 ) { res = res * digSum ( a ) ; res = digSum ( res ) ; } a = digSum ( digSum ( a ) * digSum ( a ) ) ; n /= 2 ; } return res ; } public static void main ( String args [ ] ) { int a = 9 , n = 4 ; System . out . print ( powerDigitSum ( a , n ) ) ; } }