# How to validate time in 24-hour format using Regular Expression

Given a string str, the task is to check whether the string is valid time in 24-hour format or not by using Regular Expression

The valid time in the 24-hour format must satisfy the following conditions.

1. It should start from 0-23 or 00-23.
2. It should be followed by a ‘:'(colon).
3. It should be followed by two digits from 00 to 59.
4. It should not end with ‘am’, ‘pm’ or ‘AM’, ‘PM’.

Examples:

Input: str = “13:05”
Output: true
Explanation: The given string satisfies all the above mentioned conditions.

Input: str = “02:15”
Output: true
Explanation: The given string satisfies all the above mentioned conditions.

Input: str = “24:00”
Output: false
Explanation: The given string doesn’t be in the range of 0-23 or 00-23(i.e., hour is out of range), therefore it is not a valid time in 24-hour format.

Input: str = “10:60”
Output: false
Explanation: The given string doesn’t be in the range of 00 to 59(i.e., minute is out of range), therefore it is not a valid time in 24-hour format.

Input: str = “10:15 PM”
Output: false
Explanation: The given string end with â€˜AMâ€™ or â€˜PMâ€™, therefore it is not a valid time in 24-hour format.

Approach: This problem can be solved by using Regular Expressions.

1. Get the string.
2. Create a regular expression to check time in 24-hour format as mentioned below:
`regex = "([01]?[0-9]|2[0-3]):[0-5][0-9]";`

Where:

• ( represents the start of the group.
• [01]?[0-9] represents the time that starts with 0-9, 1-9, 00-09, 10-19.
• | represents or.
• 2[0-3] represents the time starting with 20-23.
• ) represents the end of the group.

• : represents the time that should be followed by a colon(:).
• [0-5][0-9] represents the time followed by 00 to 59
1. Match the given string with the regex, in Java, this can be done by using Pattern.matcher().
2. Return true if the string matches with the given regex, else return false.

Below is the implementation of the above approach:

## C++

 `// C++ program to validate` `// time in 24-hour format` `// using Regular Expression` `#include ` `#include ` `using` `namespace` `std;`   `// Function to validate time in 24-hour format` `bool` `isValidTime(string str)` `{`   `  ``// Regex to check valid time in 24-hour format` `  ``const` `regex pattern(``"([01]?[0-9]|2[0-3]):[0-5][0-9]"``);`   `  ``// If the time in 24-hour format` `  ``// is empty return false` `  ``if` `(str.empty())` `  ``{` `     ``return` `false``;` `  ``}`   `  ``// Return true if the time in 24-hour format` `  ``// matched the ReGex` `  ``if``(regex_match(str, pattern))` `  ``{` `    ``return` `true``;` `  ``}` `  ``else` `  ``{` `    ``return` `false``;` `  ``}` `}`   `// Driver Code` `int` `main()` `{` `  `  `  ``// Test Case 1:` `  ``string str1 = ``"13:05"``;` `  ``cout << str1 + ``": "``<< isValidTime(str1) << endl;`   `  ``// Test Case 2:` `  ``string str2 = ``"02:15"``;` `  ``cout << str2 + ``": "``<< isValidTime(str2) << endl;`   `  ``// Test Case 3:` `  ``string str3 = ``"24:00"``;` `  ``cout << str3 + ``": "``<< isValidTime(str3) << endl;`   `  ``// Test Case 4:` `  ``string str4 = ``"10:60"``;` `  ``cout << str4 + ``": "``<< isValidTime(str4) << endl;`   `  ``// Test Case 5:` `  ``string str5 = ``"10:15 PM"``;` `  ``cout << str5 + ``": "``<< isValidTime(str5) << endl;`   `  ``return` `0;` `}`   `// This code is contributed by yuvraj_chandra`

## Java

 `// Java program to validate the time in` `// 24-hour format using Regular Expression.`   `import` `java.util.regex.*;`   `class` `GFG {`   `    ``// Function to validate the time in 24-hour format` `    ``public` `static` `boolean` `isValidTime(String time)` `    ``{`   `        ``// Regex to check valid time in 24-hour format.` `        ``String regex = ``"([01]?[0-9]|2[0-3]):[0-5][0-9]"``;`   `        ``// Compile the ReGex` `        ``Pattern p = Pattern.compile(regex);`   `        ``// If the time is empty` `        ``// return false` `        ``if` `(time == ``null``) {` `            ``return` `false``;` `        ``}`   `        ``// Pattern class contains matcher() method` `        ``// to find matching between given time` `        ``// and regular expression.` `        ``Matcher m = p.matcher(time);`   `        ``// Return if the time` `        ``// matched the ReGex` `        ``return` `m.matches();` `    ``}`   `    ``// Driver Code.` `    ``public` `static` `void` `main(String args[])` `    ``{`   `        ``// Test Case 1:` `        ``String str1 = ``"13:05"``;` `        ``System.out.println(str1 + ``": "` `                           ``+ isValidTime(str1));`   `        ``// Test Case 2:` `        ``String str2 = ``"02:15"``;` `        ``System.out.println(str2 + ``": "` `                           ``+ isValidTime(str2));`   `        ``// Test Case 3:` `        ``String str3 = ``"24:00"``;` `        ``System.out.println(str3 + ``": "` `                           ``+ isValidTime(str3));`   `        ``// Test Case 4:` `        ``String str4 = ``"10:60"``;` `        ``System.out.println(str4 + ``": "` `                           ``+ isValidTime(str4));`   `        ``// Test Case 5:` `        ``String str5 = ``"10:15 PM"``;` `        ``System.out.println(str5 + ``": "` `                           ``+ isValidTime(str5));` `    ``}` `}`

## Python3

 `# Python3 program to validate the time in ` `# 24-hour format using Regular Expression. ` `import` `re`   `# Function to validate the time ` `# in 24-hour format ` `def` `isValidTime(time):` `    `  `    ``# Regex to check valid time in 24-hour format. ` `    ``regex ``=` `"^([01]?[0-9]|2[0-3]):[0-5][0-9]\$"``; `   `    ``# Compile the ReGex ` `    ``p ``=` `re.``compile``(regex); `   `    ``# If the time is empty ` `    ``# return false ` `    ``if` `(time ``=``=` `"") :` `        ``return` `False``;` `        `  `    ``# Pattern class contains matcher() method` `    ``# to find matching between given time ` `    ``# and regular expression.` `    ``m ``=` `re.search(p, time);` `    `  `    ``# Return True if the time` `    ``# matched the ReGex otherwise False` `    ``if` `m ``is` `None` `:` `        ``return` `False``;` `    ``else` `:` `        ``return` `True` `        `  `# Driver Code. ` `if` `__name__ ``=``=` `"__main__"` `:` `    `  `    ``# Test Case 1: ` `    ``str1 ``=` `"13:05"``; ` `    ``print``(str1, ``": "``, isValidTime(str1)); `   `    ``# Test Case 2: ` `    ``str2 ``=` `"02:15"``; ` `    ``print``(str2, ``": "``, isValidTime(str2));` `    `  `    ``# Test Case 3:` `    ``str3 ``=` `"24:00"``;` `    ``print``(str3, ``": "``, isValidTime(str3));` `    `  `    ``# Test Case 4:` `    ``str4 ``=` `"10:60"``;` `    ``print``(str4, ``": "``, isValidTime(str4));` `    `  `    ``# Test Case 5:` `    ``str5 ``=` `"10:15 PM"``;` `    ``print``(str5, ``": "``, isValidTime(str5)); `   `# This code is contributed by AnkitRai01`

## C#

 `// C# program to validate the ` `//  Time in 24-hour format` `//using Regular Expressions` `using` `System;` `using` `System.Text.RegularExpressions;` `class` `GFG` `{`   `  ``// Main Method` `  ``static` `void` `Main(``string``[] args)` `  ``{`   `    ``// Input strings to Match` `    ``// Time in 24-hour format` `    ``string``[] str={``"13:05"``,``"02:15"` `,``"24:00"``,``"10:60"``,``"10:15 PM"``};` `    ``foreach``(``string` `s ``in` `str) {` `      ``Console.WriteLine( isValidTime(s) ? ``"true"` `: ``"false"``); ` `    ``}` `    ``Console.ReadKey(); }`   `  ``// method containing the regex` `  ``public` `static` `bool` `isValidTime(``string` `str)` `  ``{` `    ``string` `strRegex = ``@"^([01]?[0-9]|2[0-3]):[0-5][0-9]\$"``;` `    ``Regex re = ``new` `Regex(strRegex);` `    ``if` `(re.IsMatch(str))` `      ``return` `(``true``);` `    ``else` `      ``return` `(``false``);` `  ``}` `}`   `// This code is contributed by Rahul Chauhan`

## Javascript

 `// Javascript program to validate the time in` `// 24-hour format using Regular Expression.`   `// Function to validate the` `// time in` `// 24-hour format ` `function` `isValidTime(str) {` `    ``// Regex to check valid` `    ``// time in 24-hour format` `    ``let regex = ``new` `RegExp(/^([01]\d|2[0-3]):?([0-5]\d)\$/);`   `    ``//  if str ` `    ``// is empty return false` `    ``if` `(str == ``null``) {` `        ``return` `"false"``;` `    ``}`   `    ``// Return true if the str` `    ``// matched the ReGex` `    ``if` `(regex.test(str) == ``true``) {` `        ``return` `"true"``;` `    ``}` `    ``else` `{` `        ``return` `"false"``;` `    ``}` `}`   `// Driver Code` `// Test Case 1:` `let str1 = ``"13:05"``;` `console.log(isValidTime(str1));`   `// Test Case 2:` `let str2 = ``"02:15"``;` `console.log(isValidTime(str2));`   `// Test Case 3:` `let str3 = ``"24:00"``;` `console.log(isValidTime(str3));`   `// Test Case 4:` `let str4 = ``"10:60"``;` `console.log(isValidTime(str4));`   `// Test Case 5:` `let str5 = ``"10:15 PM"``;` `console.log(isValidTime(str5));`   `// This code is contributed by Rahul Chauhan`

Output:

```13:05: true
02:15: true
24:00: false
10:60: false
10:15 PM: false```

Time Complexity: O(N) for each test case, where N is the length of the given string.
Auxiliary Space: O(1)