Find total number of distinct years from a string

Given a string containing the words and dates, the task is to find the total number of distinct years mentioned in that string. 
Note: Assuming that the date will be in ‘DD-MM-YYYY’ format. 

Examples:

Input:  str = “UN was established on 24-10-1945. India got freedom on 15-08-1947.”
Output: 2
Explanation: 2 distinct years i.e. 1945 and 1947 have been referenced.

Input: str = “Soon after the world war 2 ended on 02-09-1945. The UN was established on 24-10-1945.”
Output: 1
Explanation: Only 1 Year, i.e 1945 has been referenced .

Approach:

1. Start traversing the string.
2. Check if the current character is a digit. Store it in another string, i.e. dateString.
3. Check if the current character is ‘-‘, then remove the characters stored in the dateString.
4. Check if the length of the dateString is equal to 4, then it means that it is a year.
5. Store that year in an unordered_set.
6. Return the size of the unordered_set as it contains only unique values.

Note: For Python, ‘(\d+-\d+-\d+)’ can be used in place of ‘[0-9][0-9]-[0-9][0-9]-[0-9][0-9][0-9][0-9]’ as an alternate regular expression.

Below is the implementation of the above approach:  

C++

// C++ Program to find the total
// number of distinct years
#include <bits/stdc++.h>
using namespace std;

// function to find the total
// number of distinct years
int distinct_year(string str)
{
    string str2 = "";

    unordered_set<string> uniqueDates;

    for (int i = 0; i < str.length(); i++) {

        if (isdigit(str[i])) {
            str2.push_back(str[i]);
        }

        // if we found - then clear the str2
        else if (str[i] == '-') {
            str2.clear();
        }

        // if length of str2 becomes 4
        // then store it in a set
        else if (str2.length() == 4) {
            uniqueDates.insert(str2);
            str2.clear();
        }

        // else clear the string.
        else{
           str2.clear();
        }
    }

    // return the size of set
    return uniqueDates.size();
}

// Driver code
int main()
{
    string str = "UN was established on 24-10-1945."
                 "India got freedom on 15-08-1947.";

    cout << distinct_year(str);

    return 0;
}

Java

import java.util.HashSet;
import java.util.Set;

// Java Program to find the total
// number of distinct years
public class GFG {

// function to find the total
// number of distinct years
    static int distinct_year(String str) {
        String str2 = "";

        Set<String> uniqueDates = new HashSet<>();

        for (int i = 0; i < str.length(); i++) {

            if (Character.isDigit(str.charAt(i))) {
                str2 += (str.charAt(i));
            }

            // if we found - then clear the str2
            if (str.charAt(i) == '-') {
                str2 = "";
            }

            // if length of str2 becomes 4
            // then store it in a set
            if (str2.length() == 4) {
                uniqueDates.add(str2);
                str2 = "";
            }
        }

        // return the size of set
        return uniqueDates.size();
    }

// Driver code
    static public void main(String[] args) {
        String str = "UN was established on 24-10-1945."
                + "India got freedom on 15-08-1947.";

        System.out.println(distinct_year(str));
    }
}

Python3

# Python3 Program to find the total
# number of distinct years

# function to find the total
# number of distinct years
import re


def distinct_years(str):
    matches = re.findall(r'(\d+-\d+-\d+)', str)  # regex
    # extracting distinct years
    years = set(i[-4:] for i in matches)
    return len(years)


# Driver code
if __name__ == "__main__":
    str = "UN was established on 24-10-1945.\
        India got freedom on 15-08-1947."

    print(distinct_years(str))

# This code is contributed by
# kshitijmagare19

C#

// C# Program to find the total
// number of distinct years
using System;
using System.Collections.Generic;

class GFG
{

    // function to find the total
    // number of distinct years
    static int distinct_year(String str)
    {
        String str2 = "";

        HashSet<String> uniqueDates = new HashSet<String>();

        for (int i = 0; i < str.Length; i++)
        {
            if (char.IsDigit(str[i]))
            {
                str2 += (str[i]);
            }

            // if we found - then clear the str2
            if (str[i] == '-')
            {
                str2 = "";
            }

            // if length of str2 becomes 4
            // then store it in a set
            if (str2.Length == 4)
            {
                uniqueDates.Add(str2);
                str2 = "";
            }
        }

        // return the size of set
        return uniqueDates.Count;
    }

    // Driver code
    static public void Main(String[] args)
    {
        String str = "UN was established on 24-10-1945." +
                     "India got freedom on 15-08-1947.";

        Console.WriteLine(distinct_year(str));
    }
}

// This code is contributed by Princi Singh

Javascript

<script>

// Javascript Program to find the total
// number of distinct years

// function to find the total
// number of distinct years
function distinct_year(str)
{
    var str2 = "";

    var uniqueDates = new Set();

    for (var i = 0; i < str.length; i++) {

        if (parseInt(str[i])) {
            str2+=(str[i]);
        }

        // if we found - then clear the str2
        if (str[i] == '-') {
            str2 = "";
        }

        // if length of str2 becomes 4
        // then store it in a set
        if (str2.length == 4) {
            uniqueDates.add(str2);
            str2 = "";
        }
    }

    // return the size of set
    return uniqueDates.size;
}

// Driver code
var str = "UN was established on 24-10-1945." +
             "India got freedom on 15-08-1947.";
document.write( distinct_year(str));

</script>

Output

2

Time Complexity: O(n), where n is the size of the given string.
Auxiliary Space: O(n)