Convert time from 24 hour clock to 12 hour clock format

Given a time in a 24-hour clock (military time), convert it to a 12-hour clock format.

Note: Midnight is 00:00:00 on a 24-hour clock and 12:00:00 AM on a 12-hour clock. Noon is 12:00:00 on 24-hour clock and 12:00:00 PM on 12-hour clock.

A string will be given of the format hh:mm: ss and output should be in the format hh:mm: ss AM or hh:mm: ss PM in a 12hour clock. Here hh represents an hour, mm represents minutes and ss represents seconds.

Examples: 

Input : 17:35:20
Output : 5:35:20 PM

Input : 00:10:24
Output : 12:10:24 AM

The approach to solving this problem requires some observations. First that the minutes and seconds will be the same in both cases. The only change will be in the hours and according to that Meridien will be appended to the string. For hours, first, convert it from string to int datatype, then take its modulo with 12 and that will be our hours in 12-hour format. Still, there will be a case when the hour becomes 00 i.e (12 or 00 in 24-hour format) which we need to handle separately.

Below is the implementation of the above approach: 

C++

// CPP program to convert time from 24 hour
// to 12 hour format

#include <bits/stdc++.h>

using namespace std;

// Convert Function which takes in
// 24hour time and convert it to
// 12 hour format
void convert12(string str)
{
    // Get Hours
    int h1 = (int)str[0] - '0';
    int h2 = (int)str[1] - '0';

    int hh = h1 * 10 + h2;

    // Finding out the Meridien of time
    // ie. AM or PM
    string Meridien;
    if (hh < 12) {
        Meridien = "AM";
    }
    else
        Meridien = "PM";

    hh %= 12;

    // Handle 00 and 12 case separately
    if (hh == 0) {
        cout << "12";

        // Printing minutes and seconds
        for (int i = 2; i < 8; ++i) {
            cout << str[i];
        }
    }
    else {
        cout << hh;
        // Printing minutes and seconds
        for (int i = 2; i < 8; ++i) {
            cout << str[i];
        }
    }

    // After time is printed
    // cout Meridien
    cout << " " << Meridien << '\n';
}

// Driver code
int main()
{
    // 24 hour format
    string str = "17:35:20";

    convert12(str);

    return 0;
}

Java

// Java program to convert time from 24 hour
// to 12 hour format

import java.util.*;
// Convert Function which takes in
// 24hour time and convert it to
// 12 hour format
class GFG
{

static void convert12(String str)
{
// Get Hours
    int h1 = (int)str.charAt(0) - '0';
    int h2 = (int)str.charAt(1)- '0';

    int hh = h1 * 10 + h2;

    // Finding out the Meridien of time
    // ie. AM or PM
    String Meridien;
    if (hh < 12) {
        Meridien = "AM";
    }
    else
        Meridien = "PM";

    hh %= 12;

    // Handle 00 and 12 case separately
    if (hh == 0) {
        System.out.print("12");

        // Printing minutes and seconds
        for (int i = 2; i < 8; ++i) {
        System.out.print(str.charAt(i));
        }
    }
    else {
        System.out.print(hh);
        // Printing minutes and seconds
        for (int i = 2; i < 8; ++i) {
        System.out.print(str.charAt(i));
        }
    }

    // After time is printed
    // cout Meridien
System.out.println(" "+Meridien);
}

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

// 24 hour format
    String str = "17:35:20";
    convert12(str);

}
}

Python3

# Python program to convert time from 24 hour
# to 12 hour format

# Convert Function which takes in
# 24hour time and convert it to
# 12 hour format
def convert12(str):

    # Get Hours
    h1 = ord(str[0]) - ord('0');
    h2 = ord(str[1]) - ord('0');

    hh = h1 * 10 + h2;

    # Finding out the Meridien of time
    # ie. AM or PM
    Meridien="";
    if (hh < 12):
        Meridien = "AM";
    else:
        Meridien = "PM";

    hh %= 12;

    # Handle 00 and 12 case separately
    if (hh == 0):
        print("12", end = "");

        # Printing minutes and seconds
        for i in range(2, 8):
            print(str[i], end = "");

    else:
        print(hh,end="");

        # Printing minutes and seconds
        for i in range(2, 8):
            print(str[i], end = "");

    # After time is printed
    # cout Meridien
    print(" " + Meridien);

# Driver code
if __name__ == '__main__':

    # 24 hour format
    str = "17:35:20";
    convert12(str);

# This code is contributed by 29AjayKumar

C#

// C# program to convert time from 24 hour
// to 12 hour format

using System;
// Convert Function which takes in
// 24hour time and convert it to
// 12 hour format
class GFG
{

static void convert12(string str)
{
// Get Hours
    int h1 = (int)str[0] - '0';
    int h2 = (int)str[1]- '0';

    int hh = h1 * 10 + h2;

    // Finding out the Meridien of time
    // ie. AM or PM
    string Meridien;
    if (hh < 12) {
        Meridien = "AM";
    }
    else
        Meridien = "PM";

    hh %= 12;

    // Handle 00 and 12 case separately
    if (hh == 0) {
        Console.Write("12");

        // Printing minutes and seconds
        for (int i = 2; i < 8; ++i) {
        Console.Write(str[i]);
        }
    }
    else {
        Console.Write(hh);
        // Printing minutes and seconds
        for (int i = 2; i < 8; ++i) {
        Console.Write(str[i]);
        }
    }

    // After time is printed
    // cout Meridien
Console.WriteLine(" "+Meridien);
}

//Driver code
public static void Main()
{

// 24 hour format
    string str = "17:35:20";
    convert12(str);

}
}

PHP

<?php
// PHP program to convert time
// from 24 hour to 12 hour format

// Convert Function which takes
// in 24hour time and convert it
// to 12 hour format
function convert12($str)
{
    // Get Hours
    $h1 = $str[0] - '0';
    $h2 = $str[1] - '0';

    $hh = $h1 * 10 + $h2;

    // Finding out the Meridien
    // of time ie. AM or PM
    $Meridien;
    if ($hh < 12)
    {
        $Meridien = "AM";
    }
    else
        $Meridien = "PM";

    $hh %= 12;

    // Handle 00 and 12
    // case separately
    if ($hh == 0)
    {
        echo "12";

        // Printing minutes and seconds
        for ($i = 2; $i < 8; ++$i)
        {
            echo $str[$i];
        }
    }
    else
    {
        echo $hh;

        // Printing minutes and seconds
        for ($i = 2; $i < 8; ++$i)
        {
            echo $str[$i];
        }
    }

    // After time is printed
    // cout Meridien
    echo " " , $Meridien;
}

// Driver code

// 24 hour format
$str = "17:35:20";

convert12($str);

// This code is contributed
// by ajit
?>

Javascript

<script>
// javascript program to convert time from 24 hour
// to 12 hour format

// Convert Function which takes in
// 24hour time and convert it to
// 12 hour format
function convert12(str)
{

    // Get Hours
   var h1 = Number(str[0] - '0');
    var h2 = Number(str[1] - '0');

    var hh = h1 * 10 + h2;

    // Finding out the Meridien of time
    // ie. AM or PM
    var Meridien;

    if (hh < 12) {
        Meridien = "AM";
    }
    else
        Meridien = "PM";

    hh %= 12;

    // Handle 00 and 12 case separately
    if (hh == 0) {
        document.write("12");

        // Printing minutes and seconds
        for (var i = 2; i < 8; ++i) {
        document.write(str[i]);
        }
    }
    else {
        document.write(hh);
        // Printing minutes and seconds
        for (var i = 2; i < 8; ++i) {
        document.write(str[i]);
        }
    }

    // After time is printed
    // cout Meridien

document.write(" "+Meridien);
}

// Driver code

// 24 hour format
    var str = "17:35:20";
    convert12(str);

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

Output:

5:35:20 PM

Time Complexity: O(8) = O(1)

Auxiliary Space: O(1)