Problem Statement
Given a time in 12-hour AM/PM format, convert it to military (24-hour) time.
Sample Input:
07:05:45PM
Sample Output:
19:05:45
Time Conversion HackerRank Solution
Intuition
Converting a time from a 12-hour format (AM/PM) to the military 24-hour format might sound straightforward at first glance, but there are a few intricacies to consider:
AM/PM Designation
This is the primary differentiator between the two-time formats. The presence of “AM” or “PM” at the end of the time string clearly indicates the 12-hour format. This designation affects how we interpret the hours.
The Hour Component (hh):
- In a 12-hour format:
- 12:00 AM represents midnight and 12:00 PM represents noon.
- The hours are identical in both formats for times from 01:00 AM to 11:59 AM.
- For times from 01:00 PM to 11:59 PM, the 24-hour format requires adding 12 to the hour component.
- In a 24-hour format:
- Midnight is represented as 00:00.
- Noon remains at 12:00.
- Post-noon, the hour component increases beyond 12, up to 23.
The Minute and Second Components (mm: ss)
These remain unchanged between the two formats, so no conversion is required for them.
Given this understanding, here’s a step-by-step breakdown of the conversion:
- Extract the Components: Parse the input string to extract the hour, minute, and second components. Also, identify the AM/PM designation.
- Hour Conversion
- If the time is in the PM (except for 12:00 PM to 12:59 PM), add 12 to the hour component.
- If the time is in the AM and falls between 12:00 AM and 12:59 AM, change the hour component to 00.
- In all other cases, the hour component remains unchanged.
- Reassemble the Time: Using the possibly modified hour component and the unchanged minute and second components, construct the time string in the 24-hour format.
Code Implementation
C
// Time Conversion: HackerRank Problem C Solution
#include <stdio.h>
#include <string.h>
int main() {
char time[10];
scanf("%s", time);
// Extract hours, minutes, and seconds from the input
int hh, mm, ss;
sscanf(time, "%02d:%02d:%02d", &hh, &mm, &ss);
// Check if the time is PM, but not 12:00 PM
if (strstr(time, "PM") && hh != 12) {
hh += 12;
}
// Check if the time is AM and exactly 12:00 AM
if (strstr(time, "AM") && hh == 12) {
hh = 0;
}
// Print the result in 24-hour format
printf("%02d:%02d:%02d", hh, mm, ss);
return 0;
}C++
// Time Conversion: HackerRank Problem C++ Solution
#include <iostream>
#include <string>
#include <iomanip>
int main() {
// Read the input time in a 12-hour format
std::string time;
std::cin >> time;
// Extract hour, minute, and second components from the input string
int hh = std::stoi(time.substr(0, 2));
int mm = std::stoi(time.substr(3, 2));
int ss = std::stoi(time.substr(6, 2));
// Extract AM/PM designation
std::string period = time.substr(8, 2);
// Convert 12-hour format to 24-hour format
if (period == "PM" && hh != 12) {
hh += 12;
}
if (period == "AM" && hh == 12) {
hh = 0;
}
// Print the result in 24-hour format
std::cout << std::setw(2) << std::setfill('0') << hh << ":"
<< std::setw(2) << std::setfill('0') << mm << ":"
<< std::setw(2) << std::setfill('0') << ss;
return 0;
}Java
// Time Conversion: HackerRank Problem Java Solution
import java.util.Scanner;
public class TimeConversion {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
// Read the input time in a 12-hour format
String time = sc.nextLine();
sc.close();
// Extract hour, minute, and second components from the input string
int hh = Integer.parseInt(time.substring(0, 2));
int mm = Integer.parseInt(time.substring(3, 5));
int ss = Integer.parseInt(time.substring(6, 8));
// Extract AM/PM designation
String period = time.substring(8, 10);
// Convert 12-hour format to 24-hour format
if (period.equals("PM") && hh != 12) {
hh += 12;
}
if (period.equals("AM") && hh == 12) {
hh = 0;
}
// Print the result in 24-hour format
System.out.printf("%02d:%02d:%02d", hh, mm, ss);
}
}Python
# Time Conversion: HackerRank Problem Python Solution
# Read the input time in a 12-hour format
time = input()
# Split the input string to extract hour, minute, and second components
hh, mm, ss = map(int, time[:-2].split(':'))
# Extract AM/PM designation
period = time[-2:]
# Convert 12-hour format to 24-hour format
if period == "PM" and hh != 12:
hh += 12
if period == "AM" and hh == 12:
hh = 0
# Print the result in a 24-hour format
print(f"{hh:02}:{mm:02}:{ss:02}")Output:
For the input 07:05:45PM, the output will be 19:05:45.Dry Run and Code Explanation
- Consider the input 07:05:45PM.
- Extract the hours, minutes, and seconds using sscanf(). So, hh = 7, mm = 5, and ss = 45.
- Check if the time string contains “PM” and the hour is not 12. If true, add 12 to the hours. Here, since the time is 07:05:45PM, the hour becomes 7 + 12 = 19.
- If the time string contains “AM” and the hour is 12, set the hour to 0. This handles the edge case of 12:xx:xxAM.
- Finally, print the hours, minutes, and seconds in 24-hour format. The result is 19:05:45.
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