如何使用正则表达式以12小时格式验证时间

给定字符串str ，任务是使用正则表达式检查字符串是否为12小时格式的有效时间。
12小时格式的有效时间必须满足以下条件：

1. 它应从1、2，…9或10、11、12开始。
2. 后面应跟一个冒号(:)。
3. 在其后应是两位数，介于00到59之间。
4. 它应该只允许一个空格，尽管这是可选的。
5. 它应以“ am”，“ pm”或“ AM”，“ PM”结尾。

例子：

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. 

方法：可以使用正则表达式解决此问题。

1. 获取字符串。
2. 创建一个正则表达式以12小时格式检查时间，如下所述：

regex = "(1[012]|[1-9]):[0-5][0-9](\\s)?(?i)(am|pm)";

1. 在哪里：
   • (代表群组的开始。
   • 1 [012] | [1-9]代表以10、11、12或1、2 …开头的时间。 9
   • )代表组的结尾。
   • ：表示时间后必须跟冒号(:)。
   • [0-5] [0-9]表示时间，后跟00至59。
   • (\\ s)?代表空白，时间后面是空白，这是可选的。
   • (?i)表示不区分大小写，“ am”，“ pm”或“ AM”，“ PM”分别相同。
   • (am | pm)表示时间应以“ am”，“ pm”或“ AM”，“ PM”结尾。
2. 将给定的字符串与正则表达式匹配，在Java，这可以通过使用Pattern.matcher()来完成。
3. 如果字符串与给定的正则表达式匹配，则返回true；否则返回false。

下面是上述方法的实现：

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
// time in 12-hour format
// using Regular Expression
#include 
#include 
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

输出

true
true
false
false