Skip to content
Related Articles

Related Articles

Improve Article
Find M-th number whose repeated sum of digits of a number is N
  • Last Updated : 27 May, 2021

Given two positive integers N and M. The task is to find M-th number whose sum of digits of a number until sum becomes single digit is N. 
Examples: 
 

Input: N = 1, M = 3
Output: 19 
The first two numbers being 1 and 9.

Input: N = 2, M = 5
Output:  38 
The first four numbers being 2, 11, 20 and 29.

 

A naive approach is to iterate for all numbers and keep a count of number whose sum returns N. 
An efficient approach is to find the summation of digits till it becomes single digits in O(1) that has been discussed here. Hence the formula to find M-th number will be: 
 

Mth number: (M-1)*9 + N

Below is the implementation of the above approach: 
 

C++




// C++ program to Find m-th number whose
// sum of digits of a number until
// sum becomes single digit is N
#include <bits/stdc++.h>
using namespace std;
 
// Function to find the M-th
// number whosesum till one digit is N
int findNumber(int n, int m)
{
    int num = (m - 1) * 9 + n;
    return num;
}
 
// Driver Code
int main()
{
 
    int n = 2, m = 5;
    cout << findNumber(n, m);
    return 0;
}

Java




// Java program to Find m-th number whose
// sum of digits of a number until
// sum becomes single digit is N
class GFG
{
 
// Function to find the M-th
// number whosesum till one digit is N
static int findNumber(int n, int m)
{
    int num = (m - 1) * 9 + n;
    return num;
}
 
// Driver Code
public static void main(String args[])
{
    int n = 2, m = 5;
    System.out.print(findNumber(n, m));
}
}
 
// This code is contributed
// by Akanksha Rai

Python3




# Python3 program to Find m-th number
# whose sum of digits of a number
# until sum becomes single digit is N
 
# Function to find the M-th
# number whosesum till one digit is N
def findNumber(n, m) :
     
    num = (m - 1) * 9 + n;
    return num;
 
# Driver Code
if __name__ == "__main__" :
 
    n = 2 ;
    m = 5 ;
    print(findNumber(n, m))
     
# This code is contributed by Ryuga

C#




// C# program to Find m-th number whose
// sum of digits of a number until
// sum becomes single digit is N
using System;
 
class GFG
{
 
// Function to find the M-th
// number whosesum till one digit is N
static int findNumber(int n, int m)
{
    int num = (m - 1) * 9 + n;
    return num;
}
 
// Driver Code
public static void Main()
{
    int n = 2, m = 5;
    Console.Write(findNumber(n, m));
}
}
 
// This code is contributed
// by Akanksha Rai

PHP




<?php
// PHP program to Find m-th number whose
// sum of digits of a number until
// sum becomes single digit is N
 
// number whosesum till one digit is N
function findNumber($n, $m)
{
    $num = ($m - 1) * 9 + $n;
    return $num;
}
 
// Driver Code
$n = 2; $m = 5;
echo findNumber($n, $m);
 
// This code is contributed
// by Akanksha Rai
?>

Javascript




<script>
 
// JavaScript program to Find m-th number whose
// sum of digits of a number until
// sum becomes single digit is N   
 
    // Function to find the M-th
    // number whosesum till one digit is N
    function findNumber(n , m) {
        var num = (m - 1) * 9 + n;
        return num;
    }
 
    // Driver Code
     
        var n = 2, m = 5;
        document.write(findNumber(n, m));
 
// This code contributed by Rajput-Ji
 
</script>
Output: 
38

 

Attention reader! Don’t stop learning now. Get hold of all the important mathematical concepts for competitive programming with the Essential Maths for CP Course at a student-friendly price. To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.




My Personal Notes arrow_drop_up
Recommended Articles
Page :