Extracting all present dates in any given String using Regular Expressions

Given a string Str, the task is to extract all the present dates from the string. Dates can be in the format i.e., mentioned below:

• DD-MM-YYYY
• YYYY-MM-DD
• DD Month YYYY

Examples:

Input: Str = “The First Version was released on 12-07-2008.The next Release will come on 12 July 2009. The due date for payment is  2023-09-1. India gained its freedom on 15 August 1947 which was a Friday. Republic Day is a public holiday in India where the country marks and celebrates the date on which the Constitution of India came into effect on 26-1-1950.”
Output: 12-07-2008
12 July 2009
2023-09-1
15 August 1947
26-1-1950

Approach: The problem can be solved based on the following idea:

Create a regex pattern to validate the number as written below:   
regex = “\\d{2} – \\d{2} – \\d{4}”, 
           “[0 – 9]{2}[/]{1}[0 – 9]{2}[/]{1}[0 – 9]{4}”, 
           “\\d{1, 2} – (January|February|March|April|May|June|July|August|September|October|November|December)-\\d{4}”, 
           “\\d{4} – \\d{1, 2} – \\d{1, 2}”, 
           “[0 – 9]{1, 2}\\s(January|February|March|April|May|June|July|August|September|October|November|December)\\s\\d{4}”, 
           “\\d{1, 2} – \\d{1, 2} – \\d{4}”

Where,

• [d]{2}: This pattern will match two of the preceding items if they are Digits or not.
• |: Either of them should be there

Follow the below steps to implement the idea:

• Create a regex expression to extract all the present dates from the string.
• Use Pattern class to compile the regex formed.
• Use the matcher function to find.
• If it is valid, return true. Otherwise, return false.

Below is the code implementation of the above-discussed approach:

C++

// C++ code for the above approach
#include <iostream>
#include <regex>

using namespace std;

// Driver Code
int main() {

      // String containing in it
    string str = "The First Version was released on 12-07-2008."
                 "Next Release will might come on 12 July 2009. "
                 "The due date for payment is 2023-09-1."
                 "India gained its freedom on 15 August 1947 which was a Friday."
                 "Republic Day is a public holiday in India where the country marks and celebrates "
                 "the date on which the Constitution of India came into effect on 26-1-1950.";

      // You can Add n number of date
    // formats in the below given
    // String Array.
    string strPattern[] = {
        "\\d{2}-\\d{2}-\\d{4}",
        "[0-9]{2}/{1}[0-9]{2}/{1}[0-9]{4}",
        "\\d{1,2}-(January|February|March|April|May|June|July|August|September|October|November|December)-\\d{4}",
        "\\d{4}-\\d{1,2}-\\d{1,2}",
        "[0-9]{1,2}\\s(January|February|March|April|May|June|July|August|September|October|November|December)\\s\\d{4}",
        "\\d{1,2}-\\d{1,2}-\\d{4}"
    };

    for (int i = 0; i < 6; i++) {
        regex pattern(strPattern[i]);
        sregex_iterator matcher(str.begin(), str.end(), pattern);
        sregex_iterator end;
        while (matcher != end) {
            cout << matcher->str() << endl;
            matcher++;
        }
    }

    return 0;
}

// This Code is Contributed by Prasad Kandekar(prasad264)

Java

// Java code for the above approach
import java.io.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class GFG {

    // Driver Code
    public static void main(String[] args)
    {

        // String containing in it
        String str
            = "The First Version was released on 12-07-2008."
              + "Next Release will might come on 12 July 2009. "
              + "The due date for payment is  2023-09-1."
              + "India gained its freedom on 15 August 1947 which was a Friday."
              + "Republic Day is a public holiday in India where the country marks and celebrates "
              + "the date on which the Constitution of India came into effect on 26-1-1950.";

        // You can Add n number of date
        // formats in the below given
        // String Array.
        String strPattern[] = {
            "\\d{2}-\\d{2}-\\d{4}",
            "[0-9]{2}[/]{1}[0-9]{2}[/]{1}[0-9]{4}",
            "\\d{1, 2}-(January|February|March|April|May|June|July|August|September|October|November|December)-\\d{4}",
            "\\d{4}-\\d{1, 2}-\\d{1, 2}",
            "[0-9]{1, 2}\\s(January|February|March|April|May|June|July|August|September|October|November|December)\\s\\d{4}",
            "\\d{1, 2}-\\d{1, 2}-\\d{4}"
        };

        for (int i = 0; i < strPattern.length; i++) {
            Pattern pattern
                = Pattern.compile(strPattern[i]);
            Matcher matcher = pattern.matcher(str);
            while (matcher.find()) {
                System.out.println(matcher.group());
            }
        }
    }
}

Python3

# python code for the above approach
import re

# String containing in it
str = "The First Version was released on 12-07-2008." \
      "Next Release will might come on 12 July 2009. " \
      "The due date for payment is 2023-09-1." \
      "India gained its freedom on 15 August 1947 which was a Friday." \
      "Republic Day is a public holiday in India where the country marks and celebrates " \
      "the date on which the Constitution of India came into effect on 26-1-1950."

# You can Add n number of date formats in the below given String Array.
str_pattern = [
    "\\d{2}-\\d{2}-\\d{4}",
    "[0-9]{2}/{1}[0-9]{2}/{1}[0-9]{4}",
    "\\d{1,2}-(January|February|March|April|May|June|July|August|September|October|November|December)-\\d{4}",
    "\\d{4}-\\d{1,2}-\\d{1,2}",
    "[0-9]{1,2}\\s(January|February|March|April|May|June|July|August|September|October|November|December)\\s\\d{4}",
    "\\d{1,2}-\\d{1,2}-\\d{4}"
]

for pattern in str_pattern:
    for match in re.finditer(pattern, str):
        print(match.group())

# This Code is Contributed by Prasad Kandekar(prasad264)

C#

// C# code for the above approach
using System;
using System.Text.RegularExpressions;

class GFG {
    static void Main(string[] args) {

        // String containing in it
        string str = "The First Version was released on 12-07-2008."
            + "Next Release will might come on 12 July 2009. "
            + "The due date for payment is  2023-09-1."
            + "India gained its freedom on 15 August 1947 which was a Friday."
            + "Republic Day is a public holiday in India where the country marks and celebrates "
            + "the date on which the Constitution of India came into effect on 26-1-1950.";
   // You can Add n number of date
        // formats in the below given
        // String Array.
        string[] strPattern = new string[] {
            "\\d{2}-\\d{2}-\\d{4}",
            "[0-9]{2}[/]{1}[0-9]{2}[/]{1}[0-9]{4}",
            "\\d{1, 2}-(January|February|March|April|May|June|July|August|September|October|November|December)-\\d{4}",
            "\\d{4}-\\d{1, 2}-\\d{1, 2}",
            "[0-9]{1, 2}\\s(January|February|March|April|May|June|July|August|September|October|November|December)\\s\\d{4}",
            "\\d{1, 2}-\\d{1, 2}-\\d{4}"
        };

        foreach (string pattern in strPattern) {
            MatchCollection matches = Regex.Matches(str, pattern);
            foreach (Match match in matches) {
                Console.WriteLine(match.Value);
            }
        }
    }
}

Javascript

// JavaScript code for the above approach
// String containing in it
const str = "The First Version was released on 12-07-2008." +
    "Next Release will might come on 12 July 2009. " +
    "The due date for payment is 2023-09-1." +
    "India gained its freedom on 15 August 1947 which was a Friday." +
    "Republic Day is a public holiday in India where the country marks and celebrates " +
    "the date on which the Constitution of India came into effect on 26-1-1950.";

// You can Add n number of date
// formats in the below given
// String Array.
const strPattern = [
    "\\d{2}-\\d{2}-\\d{4}",
    "[0-9]{2}/{1}[0-9]{2}/{1}[0-9]{4}",
    "\\d{1,2}-(January|February|March|April|May|June|July|August|September|October|November|December)-\\d{4}",
    "\\d{4}-\\d{1,2}-\\d{1,2}",
    "[0-9]{1,2}\\s(January|February|March|April|May|June|July|August|September|October|November|December)\\s\\d{4}",
    "\\d{1,2}-\\d{1,2}-\\d{4}"
];

for (let i = 0; i < 6; i++) {
    const pattern = new RegExp(strPattern[i], 'g');
    let matcher = str.matchAll(pattern);
    for (const match of matcher) {
        console.log(match[0]);
    }
}
// This code is contributed by Prajwal Kandekar

Output

12-07-2008
2023-09-1
12 July 2009
15 August 1947
12-07-2008
26-1-1950

Time Complexity: O(n*m), N is the length of the input string and M is the number of date formats in the strPattern array.

Space Complexity: O(k), where k is the total number of matched dates.