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

Last Updated : 15 Sep, 2023

Given an odd number in the form of a string, the task is to make the largest even number from the given number, and you are allowed to do only one swap operation.

Examples :

Input: 1235785
Output: 1535782
Explanation: Swap 2 and 5.

Input: 536425
Output: 536524
Explanation: Swap 4 and 5 to make the largest even number.

Recommended PracticeOdd to EvenTry It!

Find the first even number less than or equal to the odd number at the last index.
If found, swap both values. Else swap with the last even value in the string.
If not possible to make even, print the given string.

Implementation:

C++

// C++ program for above implementation 
#include <bits/stdc++.h> 
using namespace std; 
  
// Make the largest even number 
string makeEven(string& str) 
{ 
    int n = str.length(); 
    int even = INT_MAX, index; 
  
    // Start traversing the string 
    for (int i = 0; i < n - 1; i++) { 
  
        // Find the even number 
        if ((str[i] - '0') % 2 == 0) { 
            even = (str[i] - '0'); 
            index = i; 
        } 
  
        // Check if current even is equal to 
        // or less than the odd number 
        if (even <= (str[n - 1] - '0')) 
            break; 
    } 
  
    // Return original string if there is no 
    // even value 
    if (even == INT_MAX) 
        return str; 
  
    // Swap even and odd value 
    swap(str[index], str[n - 1]); 
  
    return str; 
} 
  
// Driver code 
int main() 
{ 
    string str = "1356425"; 
    cout << makeEven(str); 
    return 0; 
}

Java

// Java program for above implementation 
  
class GFG { 
  
    // Make the largest even number 
    static char[] makeEven(String string) 
    { 
        char[] str = string.toCharArray(); 
        int n = str.length; 
        int even = Integer.MAX_VALUE, index = 0; 
  
        // Start traversing the String 
        for (int i = 0; i < n - 1; i++) { 
  
            // Find the even number 
            if ((str[i] - '0') % 2 == 0) { 
                even = (str[i] - '0'); 
                index = i; 
            } 
  
            // Check if current even is equal to 
            // or less than the odd number 
            if (even <= (str[n - 1] - '0')) { 
                break; 
            } 
        } 
  
        // Return original String if there is no 
        // even value 
        if (even == Integer.MAX_VALUE) { 
            return str; 
        } 
  
        // Swap even and odd value 
        swap(str, index, n - 1); 
  
        return str; 
    } 
    static void swap(char[] str, int index1, int index2) 
    { 
        char temp = str[index1]; 
        str[index1] = str[index2]; 
        str[index2] = temp; 
    } 
    // Driver code 
    public static void main(String[] args) 
    { 
        String str = "1356425"; 
        System.out.print(makeEven(str)); 
    } 
} 
/*This code is contributed by PrinciRaj1992*/

Python3

# Python3 code for the above implementation 
import sys 
  
# Make the largest even number 
  
  
def makeEven(arr, n): 
  
    # index to first even no,if any 
    first_e_i = -1
  
    # index to last even no, if any 
    last_e_i = -1
  
    # index to last no 
    last_n_i = n - 1
  
    # Start traversing the String 
    for i in range(n): 
  
        # if it finds any first even no less 
        # than last digit then break the loop 
        if (int(arr[i]) % 2 == 0 and
                int(arr[i]) < int(arr[last_n_i])): 
            first_e_i = i 
            break
  
        # it finds last even no 
        if int(arr[i]) % 2 == 0: 
            last_e_i = i 
    if first_e_i != -1: 
  
        # swap even and odd value 
        (arr[first_e_i], 
         arr[last_n_i]) = (arr[last_n_i], 
                           arr[first_e_i]) 
        return arr 
    if first_e_i == -1 and last_e_i != -1: 
  
        # swap even and odd value 
        (arr[last_e_i], 
         arr[last_n_i]) = (arr[last_n_i], 
                           arr[last_e_i]) 
        return arr 
  
    # Return original String if there is 
    # no even number 
    return arr 
  
  
# Driver Code 
if __name__ == '__main__': 
    string = "1356425"
    result = "".join(makeEven(list(string), 
                              len(list(string)))) 
    print(result) 
  
# This code is contributed 
# by Vikash Kumar 37 

C#

// C# implementation of above approach 
using System; 
  
public class GFG { 
  
    // Make the largest even number 
    static char[] makeEven(String str1) 
    { 
        char[] str = str1.ToCharArray(); 
        int n = str.Length; 
        int even = int.MaxValue, index = 0; 
  
        // Start traversing the String 
        for (int i = 0; i < n - 1; i++) { 
  
            // Find the even number 
            if ((str[i] - '0') % 2 == 0) { 
                even = (str[i] - '0'); 
                index = i; 
            } 
  
            // Check if current even is equal to 
            // or less than the odd number 
            if (even <= (str[n - 1] - '0')) { 
                break; 
            } 
        } 
  
        // Return original String if there is no 
        // even value 
        if (even == int.MaxValue) { 
            return str; 
        } 
  
        // Swap even and odd value 
        swap(str, index, n - 1); 
  
        return str; 
    } 
    static void swap(char[] str, int index1, int index2) 
    { 
        char temp = str[index1]; 
        str[index1] = str[index2]; 
        str[index2] = temp; 
    } 
    // Driver code 
    public static void Main() 
    { 
        String str = "1356425"; 
        Console.WriteLine(makeEven(str)); 
    } 
} 
/*This code is contributed by PrinciRaj1992*/

PHP

<?php 
// PHP program for above implementation 
  
// Make the largest even number 
function makeEven($str) 
{ 
    $n = strlen($str); 
    $even = PHP_INT_MAX; $index; 
  
    // Start traversing the string 
    for ($i = 0; $i < $n - 1; $i++)  
    { 
  
        // Find the even number 
        if (($str[$i] - '0') % 2 == 0) 
        { 
            $even = ($str[$i] - '0'); 
            $index = $i; 
        } 
  
        // Check if current even is  
        // equal to or less than  
        // the odd number 
        if ($even <= ($str[$n - 1] - '0')) 
            break; 
    } 
  
    // Return original string if  
    // there is no even value 
    if ($even == PHP_INT_MAX) 
        return $str; 
  
    //swap the number  
    list($str[$index],  
         $str[$n - 1]) = array($str[$n - 1],  
                               $str[$index]); 
    return $str; 
} 
  
// Driver code 
$str = "1356425"; 
echo makeEven($str); 
  
// This code is contributed by ajit 
?>

Javascript

<script> 
    // Javascript program for above implementation 
      
    // Make the largest even number  
    function makeEven(string) { 
        let str = string.split(''); 
        let n = str.length; 
        let even = Number.MAX_VALUE, index = 0; 
    
        // Start traversing the String  
        for (let i = 0; i < n - 1; i++) { 
    
            // Find the even number  
            if ((str[i].charCodeAt() - '0'.charCodeAt()) % 2 == 0) { 
                even = (str[i] - '0'); 
                index = i; 
            } 
    
            // Check if current even is equal to  
            // or less than the odd number  
            if (even <= (str[n-1].charCodeAt() - '0'.charCodeAt())) { 
                break; 
            } 
        } 
    
        // Return original String if there is no  
        // even value  
        if (even == Number.MAX_VALUE) { 
            return str; 
        } 
    
        // Swap even and odd value  
        swap(str,index, n - 1); 
    
        return str.join(""); 
    } 
      
    function swap(str, index1, index2) 
    { 
      let temp = str[index1]; 
      str[index1] = str[index2]; 
      str[index2] =temp; 
    } 
      
    let str = "1356425"; 
      document.write(makeEven(str)); 
      
</script>

Output

Time Complexity: O(N)
Auxiliary Space: O(1)

Maximum possible number with the given operation

GeeksforGeeks

Improve

Article Tags :

Practice Tags :

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

C++

Java

Python3

C#

PHP

Javascript

Similar Reads

Thank You!

What kind of Experience do you want to share?