Maximize time by replacing '_' in a given 24 Hour format time

Given a string S representing a time in 24 hours format, with '_' placed at positions of some digits, the task is to find the maximum time possible by replacing the characters '_' with any digit.

Examples:

Input: S = “0_:4_”
Output: 09:39
Explanation: Replacing the characters S[1] and S[4] with '9' modifies the string to "09:49", which is the maximum time possible.

Input: S = “__:__”
Output: 23:59

Approach: The given problem can be solved by greedily selecting the digits for each '_' present in the string. Follow the steps below to solve the problem:

If the character S[0] is equal to '_' and S[1] is either '_' or is less than 4, then assign '2' to S[0]. Otherwise, assign '1' to S[0].
If the character S[1] is equal to '_' and S[0] is '2', then assign '3' to S[1]. Otherwise, assign '9' to S[1].
If the character S[3] is equal to '_', then assign '5' to S[3].
If the character S[4] is equal to '_', then assign '9' to S[4].
After completing the above steps, print the modified string S.

Below is the implementation of the above approach:

C++

// C++ program for the above approach

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

// Function to find the maximum
// time possible by replacing
// each '_' with any digit
string maximumTime(string s)
{
    // If the first character is '_'
    if (s[0] == '_') {

        // If s[1] is '_' or
        // s[1] is less than 4
        if ((s[1] == '_')
            || (s[1] >= '0'
                && s[1] < '4')) {

            // Update s[0] as 2
            s[0] = '2';
        }

        // Otherwise, update s[0] = 1
        else {
            s[0] = '1';
        }
    }

    // If s[1] is equal to '_'
    if (s[1] == '_') {

        // If s[0] is equal to '2'
        if (s[0] == '2') {
            s[1] = '3';
        }

        // Otherwise
        else {
            s[1] = '9';
        }
    }

    // If S[3] is equal to '_'
    if (s[3] == '_') {
        s[3] = '5';
    }

    // If s[4] is equal to '_'
    if (s[4] == '_') {
        s[4] = '9';
    }

    // Return the modified string
    return s;
}

// Driver Code
int main()
{
    string S = "0_:4_";
    cout << maximumTime(S);

    return 0;
}

Java

// Java program for the above approach
class GFG{
    
// Function to find the maximum
// time possible by replacing
// each '_' with any digit
static void maximumTime(String str)
{
    char []s = str.toCharArray();
    
    // If the first character is '_'
    if (s[0] == '_') 
    {
        
        // If s[1] is '_' or
        // s[1] is less than 4
        if ((s[1] == '_') || 
            (s[1] >= '0' && s[1] < '4')) 
        {
            
            // Update s[0] as 2
            s[0] = '2';
        }

        // Otherwise, update s[0] = 1
        else 
        {
            s[0] = '1';
        }
    }

    // If s[1] is equal to '_'
    if (s[1] == '_') 
    {
        
        // If s[0] is equal to '2'
        if (s[0] == '2')
        {
            s[1] = '3';
        }

        // Otherwise
        else 
        {
            s[1] = '9';
        }
    }

    // If S[3] is equal to '_'
    if (s[3] == '_') 
    {
        s[3] = '5';
    }

    // If s[4] is equal to '_'
    if (s[4] == '_')
    {
        s[4] = '9';
    }

    // Print the modified string
    for(int i = 0; i < s.length; i++)
        System.out.print(s[i]);
}

// Driver Code
static public void main (String []args)
{
    String S = "0_:4_";
    
    maximumTime(S);
}
}

// This code is contributed by AnkThon

Python3

# Python3 program for the above approach

# Function to find the maximum
# time possible by replacing
# each '_' with any digit
def maximumTime(s):
    
    s = list(s)
    # If the first character is '_'
    if (s[0] == '_'):
        
        # If s[1] is '_' or
        # s[1] is less than 4
        if ((s[1] == '_') or (s[1] >= '0' and 
                              s[1] < '4')):
                                  
            # Update s[0] as 2
            s[0] = '2'

        # Otherwise, update s[0] = 1
        else:
            s[0] = '1'

    # If s[1] is equal to '_'
    if (s[1] == '_'):
        
        # If s[0] is equal to '2'
        if (s[0] == '2'):
            s[1] = '3'

        # Otherwise
        else:
            s[1] = '9'

    # If S[3] is equal to '_'
    if (s[3] == '_'):
        s[3] = '5'

    # If s[4] is equal to '_'
    if (s[4] == '_'):
        s[4] = '9'

    # Return the modified string
    s = ''.join(s)
    return s

# Driver Code
if __name__ == '__main__':
    
    S = "0_:4_"
    
    print(maximumTime(S))
    
# This code is contributed by ipg2016107

// C# program for the above approach
using System;

class GFG{
    
// Function to find the maximum
// time possible by replacing
// each '_' with any digit
static void maximumTime(string str)
{
    char []s = str.ToCharArray();
    
    // If the first character is '_'
    if (s[0] == '_') 
    {
        
        // If s[1] is '_' or
        // s[1] is less than 4
        if ((s[1] == '_') || 
            (s[1] >= '0' && s[1] < '4')) 
        {
            
            // Update s[0] as 2
            s[0] = '2';
        }

        // Otherwise, update s[0] = 1
        else 
        {
            s[0] = '1';
        }
    }

    // If s[1] is equal to '_'
    if (s[1] == '_') 
    {
        
        // If s[0] is equal to '2'
        if (s[0] == '2')
        {
            s[1] = '3';
        }

        // Otherwise
        else 
        {
            s[1] = '9';
        }
    }

    // If S[3] is equal to '_'
    if (s[3] == '_') 
    {
        s[3] = '5';
    }

    // If s[4] is equal to '_'
    if (s[4] == '_')
    {
        s[4] = '9';
    }

    // Print the modified string
    for(int i = 0; i < s.Length; i++)
        Console.Write(s[i]);
}

// Driver Code
static public void Main ()
{
    string S = "0_:4_";
    
    maximumTime(S);
}
}

// This code is contributed by AnkThon

JavaScript

<script>
// javascript program for the above approach

     
// Function to find the maximum
// time possible by replacing
// each '_' with any digit

     function maximumTime(str)
{
     var s = str.split("");
     
    // If the first character is '_'
    if (s[0] == '_')
    {
         
        // If s[1] is '_' or
        // s[1] is less than 4
        if ((s[1] == '_') ||
            (s[1] >= '0' && s[1] < '4'))
        {
             
            // Update s[0] as 2
            s[0] = '2';
        }
 
        // Otherwise, update s[0] = 1
        else
        {
            s[0] = '1';
        }
    }
 
    // If s[1] is equal to '_'
    if (s[1] == '_')
    {
         
        // If s[0] is equal to '2'
        if (s[0] == '2')
        {
            s[1] = '3';
        }
 
        // Otherwise
        else
        {
            s[1] = '9';
        }
    }
 
    // If S[3] is equal to '_'
    if (s[3] == '_')
    {
        s[3] = '5';
    }
 
    // If s[4] is equal to '_'
    if (s[4] == '_')
    {
        s[4] = '9';
    }
 
    // Print the modified string
    for(var i = 0; i < s.length; i++)
        document.write(s[i]);
}
 
// Driver Code
    var S = "0_:4_";    
    maximumTime(S);

// This code is contributed by bunnyram19.
</script>

// C program for above approach
#include <stdio.h>
#include <string.h>

// Function to find the maximum
// time possible by replacing
// each '_' with any digit
char* maximumTime(char s[])
{
    // If the first character is '_'
    if (s[0] == '_') {

        // If s[1] is '_' or
        // s[1] is less than 4
        if ((s[1] == '_') || (s[1] >= '0' && s[1] < '4')) {

            // Update s[0] as 2
            s[0] = '2';
        }
        else { // Otherwise, update s[0] = 1
            s[0] = '1';
        }
    }

    // If s[1] is equal to '_'
    if (s[1] == '_') {

        // If s[0] is equal to '2'
        if (s[0] == '2') {
            s[1] = '3';
        }
      // otherwise
        else { 
            s[1] = '9';
        }
    }

    // If S[3] is equal to '_'

    if (s[3] == '_') {

        s[3] = '5';
    }

    // If s[4] is equal to '_'

    if (s[4] == '_') {

        s[4] = '9';
    }

    return s; // Return the modified string
}
int main()
{
    char S[] = "0_:4_";
    printf("%s", maximumTime(S));
    return 0;
}

// This code is contributed by Tapesh (tapeshdua420)

Output

09:49

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

Maximize time by replacing '_' in a given 24 Hour format time

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