Find the n | Efficient Java program to find n - th number made of even digits only ; function to find nth number made of even digits only ; If n = 1 return 0 ; vector to store the digits when converted into base 5 ; Reduce n to n - 1 to exclude 0 ; Reduce n to base 5 number and store digits ; pushing the digits into vector ; variable to represent the number after converting it to base 5. Since the digits are be in reverse order , we traverse vector from back ; return 2 * result ( to convert digits 0 , 1 , 2 , 3 , 4 to 0 , 2 , 4 , 6 , 8. ; Driver Code
import java . util . * ; class GFG { static int findNthEvenDigitNumber ( int n ) { if ( n == 1 ) { return 0 ; } Vector < Integer > v = new Vector < > ( ) ; n = n - 1 ; while ( n > 0 ) { v . add ( n % 5 ) ; n = n / 5 ; } int result = 0 ; for ( int i = v . size ( ) - 1 ; i >= 0 ; i -- ) { result = result * 10 ; result = result + v . get ( i ) ; } return 2 * result ; } public static void main ( String [ ] args ) { System . out . println ( findNthEvenDigitNumber ( 2 ) ) ; System . out . println ( findNthEvenDigitNumber ( 10 ) ) ; } }