Number of digits in the nth number made of given four digits | Java program to count number of digits in n - th number made of given four digits . ; Efficient function to calculate number of digits in the nth number constructed by using 6 , 1 , 4 and 9 as digits in the ascending order . ; Number of digits increase after every i - th number where i increases in powers of 4. ; Driver Code
import java . io . * ; class GFG { static int number_of_digits ( int n ) { int i ; int res ; int sum = 0 ; for ( i = 4 , res = 1 ; ; i *= 4 , res ++ ) { sum += i ; if ( sum >= n ) break ; } return res ; } public static void main ( String [ ] args ) { int n = 21 ; System . out . println ( number_of_digits ( n ) ) ; } }