Largest number less than N with digit sum greater than the digit sum of N in C++

In this tutorial, we are going to write a program that finds the number less than N with digit sum greater than the digit sum of n.

Let's see the steps to solve the problem.

Write a function to find the digits sum.
Initialise n.
Write a loop that iterates from n - 1 to 1.
- Check the digits sum of current number with the digits sum of n.
- If the digits sum of current number is greater than n, then return the current number.
- Move to the next number.

Example

Let's see the code.

Live Demo

#include <bits/stdc++.h>
using namespace std;
int sumOfDigits(int n) {
   int digitsSum = 0;
   while (n > 0) {
      digitsSum += n % 10;
      n /= 10;
   }
   return digitsSum;
}
int findLargestNumber(int n) {
   int i = n - 1;
   while (i > 0) {
      if (sumOfDigits(i) > sumOfDigits(n)) {
         return i;
      }
      i--;
   }
   return -1;
}
int main() {
   int n = 75;
   cout << findLargestNumber(n) << endl;
   return 0;
}