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Odd To Even

Last Updated: 26 Feb, 2021
Difficulty: Easy


Try Problem

You are given an odd number in the form of a string, ‘S.’ Your goal is to convert the number into an even number such that the following two conditions are satisfied.

You can use swap operation over any two indices i,e you can choose two indices 'i' and 'j' and swap the digits present at S[i] and S[j]. But this operation can be used only once.

Your final even number should be the largest out of all other possible even numbers.
If it isn’t possible to make an even number print -1
Input Format:
The first line of the input contains ‘T’ denoting the number of test cases.

The first and the only line of each test case contains a string ‘S’ the odd number.
Output Format:
If it is possible to make even number print largest out of all. Else print -1

Print the result of each test case in a new line.
1 <= T <= 5
0 <= |S| <= 10^5

Time Limit : 1 sec

Approach 1

  • Since we need to convert odd numbers to even numbers, we need to first check if it is possible to do it or not, which can be done by finding even digits in the number.
  • After which if even digits exist, we need to swap all the positions with even digits with the last digit (at one’s place) to make it even and store this new string in an array of strings.
  • After storing all possible strings, we find and return the largest of them.




  • If there is no even digit in the number,  return -1.
  • Iterate over the number (string) and find positions which have even digit, then swap this position to last position (at one’s place).  Store this new string in a vector.
  • Return the largest string in the vector.
Try Problem