Find the minimum number possible by changing at most one digit

Given a positive integer N consisting only two types of digits 6 and 9, the task is to generate the minimum number possible by reversing at most one digit, that is 9 becomes 6 or vice versa.
Examples:

Input : 9996 
Output : 6996 
Explanation : 
Changing the first digit results in 6996. 
Changing the second digit results in 9696. 
Changing the third digit results in 9966. 
Changing the fourth digit results in 9999. 
Hence, the minimum number among all possibilities is 6996.
Input : 6696 
Output : 6666 
Explanation : 
Changing the first digit results in 9696. 
Changing the second digit results in 6996. 
Changing the third digit results in 6666. 
Changing the fourth digit results in 6699. 
Hence, the minimum number among all possibilities is 6666. 

Approach:
In order to solve the problem, we need to follow the steps given below: 

• First convert the given integer into a string.
• Traverse the string from left and change the very first occurrence of ‘9’ to ‘6’ and break out of the loop. If there is no occurrence of 9 in the initial string, then it is already the lowest number possible.
• Convert the final string back to the integer and print it.

Below is the implementation of the above approach: 

C++

// C++ implementation to change at most
// one digit to make the number
// as minimum as possible

#include <bits/stdc++.h>
using namespace std;

// Function to return the minimum
// possible number
int minimum69Number(int num)
{

    // Converting given number to string
    string s_num = to_string(num);

    // Traversing the string
    for (auto& c : s_num) {
        // change first 9 to 6
        if (c == '9') {
            c = '6';
            break;
        }
    }

    // Change the string back to the integer
    int result = stoi(s_num);

    // Return the final result
    return result;
}

// Driver code
int main()
{
    // Input number
    int n = 9996;

    int result = minimum69Number(n);

    // Print the result
    cout << result << endl;
}

Java

// Java implementation to change at most
// one digit to make the number
// as minimum as possible
class GFG{

// Function to return the minimum
// possible number
static int minimum69Number(int num)
{

    // Converting given number to String
    char []s_num = String.valueOf(num).toCharArray();

    // Traversing the String
    for(int i = 0; i < s_num.length; i++)
    {

       // change first 9 to 6
       if (s_num[i] == '9')
       {
           s_num[i] = '6';
           break;
       }
    }

    // Change the String back to the integer
    int result = Integer.valueOf(String.valueOf(s_num));

    // Return the final result
    return result;
}

// Driver code
public static void main(String[] args)
{

    // Input number
    int n = 9996;
    int result = minimum69Number(n);

    // Print the result
    System.out.print(result + "\n");
}
}

// This code is contributed by 29AjayKumar

Python3

# Python3 implementation to change at most
# one digit to make the number
# as minimum as possible

# Function to return the minimum
# possible number
def minimum69Number(num):

    # Converting given number to string
    s_num = str(num)

    s_num = s_num.replace('9','6', 1)

    # Change the string back to the integer
    result = int(s_num)

    # Return the final result
    return result

# Driver code
if __name__ == '__main__':

    # Input number
    n = 9996

    result = minimum69Number(n)

    # Print the result
    print(result)

# This code is contributed by Samarth

C#

// C# implementation to change at most
// one digit to make the number
// as minimum as possible
using System;

class GFG{

// Function to return the minimum
// possible number
static int minimum69Number(int num)
{

    // Converting given number to String
    char []s_num = String.Join("", num).ToCharArray();

    // Traversing the String
    for(int i = 0; i < s_num.Length; i++)
    {
       // change first 9 to 6
       if (s_num[i] == '9')
       {
           s_num[i] = '6';
           break;
       }
    }

    // Change the String back to the integer
    int result = Int32.Parse(String.Join("", s_num));

    // Return the readonly result
    return result;
}

// Driver code
public static void Main(String[] args)
{

    // Input number
    int n = 9996;
    int result = minimum69Number(n);

    // Print the result
    Console.Write(result + "\n");
}
}

// This code is contributed by sapnasingh4991

Javascript

<script>

    // JavaScript implementation to change at most
    // one digit to make the number
    // as minimum as possible

    // Function to return the minimum
    // possible number
    function minimum69Number(num)
    {

        // Converting given number to string
        let s_num = (num.toString()).split('');

        // Traversing the String
        for(let i = 0; i < s_num.length; i++)
        {

           // change first 9 to 6
           if (s_num[i] == '9')
           {
               s_num[i] = '6';
               break;
           }
        }

        // Change the String back to the integer
        let result = parseInt(s_num.join(""));

        // Return the final result
        return result;
    }

    // Driver code

    // Input number
    let n = 9996;

    let result = minimum69Number(n);

    // Print the result
   document.write(result);

</script>

Output:

6996

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