How to validate time in 12-hour format using Regular Expression
Given a string str, the task is to check whether the string is valid time in 12-hour format or not by using Regular Expression.
The valid time in a 12-hour format must satisfy the following conditions:
- It should start from 1, 2, … 9 or 10, 11, 12.
- It should be followed by a colon(:).
- It should be followed by two digits between 00 to 59.
- It should only allow one white space, although this is optional.
- It should end with ‘am’, ‘pm’ or ‘AM’, ‘PM’.
Examples:
Input: str = 12:15 AM
Output: true
Explanation: The given string satisfies all the above mentioned conditions.Input: str = 9:45PM
Output: true
Explanation: The given string satisfies all the above mentioned conditions.Input: str = 1:15
Output: false
Explanation: The given string does not end with ‘AM’ or ‘PM’, therefore it is not a valid time in 12-hour format.Input: str = 17:30 PM
Output: false
Explanation: The given string does not have hours in between 1 to 12, therefore it is not a valid time in 12-hour format.
Approach: This problem can be solved by using Regular Expression.
- Get the string.
- Create a regular expression to check time in 12-hour format as mentioned below:
regex = "(1[012]|[1-9]):[0-5][0-9](\\s)?(?i)(am|pm)";
Where:
- ( represents the start of the group.
- 1[012]|[1-9] represents time start with 10, 11, 12 or 1, 2, …. 9
- ) represents the end of the group.
- : represents time must be followed by colon(:).
- [0-5][0-9] represents the time followed by 00 to 59.
- (\\s)? represents white space, time followed by a white space which is optional.
- (?i) represents case insensitive, ‘am’, ‘pm’ or ‘AM’, ‘PM’ are same respectively.
- (am|pm) represents time should end with ‘am’, ‘pm’ or ‘AM’, ‘PM’.
- Match the given string with the regex, in Java this can be done by using Pattern.matcher().
- 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 12-hour format // using Regular Expression #include <iostream> #include <regex> using namespace std; // Function to validate time in 12-hour format bool isValidTime(string str) { // Regex to check valid time in 12-hour format const regex pattern( "((([1-9])|(1[0-2])):([0-5])([0-9])(\\s)(A|P)M)" ); // If the time in 12-hour format // is empty return false if (str.empty()) { return false ; } // Return true if the time in 12-hour format // matched the ReGex if (regex_match(str, pattern)) { return true ; } else { return false ; } } // Driver Code int main() { // Test Case 1: string str1 = "12:15 AM" ; cout << isValidTime(str1) << endl; // Test Case 2: string str2 = "9:45 PM" ; cout << isValidTime(str2) << endl; // Test Case 3: string str3 = "1:15" ; cout << isValidTime(str3) << endl; // Test Case 4: string str4 = "17:30" ; cout << isValidTime(str4) << endl; return 0; } // This code is contributed by yuvraj_chandra |
Java
// Java program to validate the time in // 12-hour format using Regular Expression. import java.util.regex.*; class GFG { // Function to validate the time in 12-hour format. public static boolean isValidTime(String time) { // Regex to check valid time in 12-hour format. String regexPattern = "(1[012]|[1-9]):" + "[0-5][0-9](\\s)" + "?(?i)(am|pm)" ; // Compile the ReGex Pattern compiledPattern = Pattern.compile(regexPattern); // 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 = compiledPattern.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 = "12:15 AM" ; System.out.println(isValidTime(str1)); // Test Case 2: String str2 = "9:45PM" ; System.out.println(isValidTime(str2)); // Test Case 3: String str3 = "1:15" ; System.out.println(isValidTime(str3)); // Test Case 4: String str4 = "17:30" ; System.out.println(isValidTime(str4)); } } |
Python3
# Python3 program to validate the time in # 12-hour format using Regular Expression. import re # Function to validate the time in 12-hour format. def isValidTime(time) : # Regex to check valid time in 12-hour format. regexPattern = "(1[012]|[1-9]):" + "[0-5][0-9](\\s)" + "?(?i)(am|pm)" ; # Compile the ReGex compiledPattern = re. compile (regexPattern); # If the time is empty # return false if (time = = None ) : return False ; # re library contains search() method # to find matching between given time # and regular expression. # Return if the time # matched the ReGex if re.search(compiledPattern,time): return True else : return False # Driver Code. if __name__ = = "__main__" : # Test Case 1: str1 = "12:15 AM" ; print (isValidTime(str1)); # Test Case 2: str2 = "9:45PM" ; print (isValidTime(str2)); # Test Case 3: str3 = "1:15" ; print (isValidTime(str3)); # Test Case 4: str4 = "17:30" ; print (isValidTime(str4)); # This code is contributed by AnkitRai01 |
C#
// C# program to validate the // Time in 12-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 12-hour format string [] str={ "12:15 AM" , "9:45PM" , "1:15" , "17:30" }; 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 = @"(1[012]|[1-9]):[0-5][0-9](\s)?(?i)(am|pm)" ; 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 // 12-hour format using Regular Expression. // Function to validate the // time in // 12-hour format function isValidTime(str) { // Regex to check valid // time in 12-hour format let regex = new RegExp(/((1[0-2]|0?[1-9]):([0-5][0-9]) ?([AaPp][Mm]))/); // 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 = "12:15 AM" ; console.log(isValidTime(str1)); // Test Case 2: let str2 = "9:45PM" ; console.log(isValidTime(str2)); // Test Case 3: let str3 = "1:15" ; console.log(isValidTime(str3)); // Test Case 4: let str4 = "17:30" ; console.log(isValidTime(str4)); // This code is contributed by Rahul Chauhan |
true true false false
Time Complexity: O(N) for each testcase, where N is the length of the given string.
Auxiliary Space: O(1)
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