Largest even number possible by using one swap operation in given number in C++

In this tutorial, we are going to write a program that finds the largest possible even number with a single swap of digits.

Let's see the steps to solve the problem.

• Initialise the number in string format.
• Iterate over the given number.
  • Find the even digit that is less than or equal to the last digit of the number.
  • Break the loop if you find the desired even digit.
• If the even digit doesn't exist, then return the given number.
• Swap the last digit with the even digit you found in the above step.
• Return the number

Example

#include <bits/stdc++.h>
using namespace std;
string getLargestEvenNumber(string number, int n) {
   int even = INT_MAX, index;
   for (int i = 0; i < n - 1; i++) {
      if ((number[i] - '0') % 2 == 0) {
         even = (number[i] - '0');
         index = i;
      }
      if (even <= (number[n - 1] - '0')) {
         break;
      }
   }
   if (even == INT_MAX) {
      return number;
   }
   swap(number[index], number[n - 1]);
   return number;
}
int main() {
   string number = "15433";
   cout << getLargestEvenNumber(number, 5) << endl;
   return 0;
}

Output

If you run the above code, then you will get the following result.

15334

Conclusion

If you have any queries in the tutorial, mention them in the comment section.