Find total number of distinct years from a string in C++ Program

In this article, we will write a C++ program to find the total number of distinct years from a string. Here, we have a string that contains the words and the dates. Our task is to find the number of distinct years mentioned.

Let's see the following example scenario to understand the problem better:

Scenario 1

Input: str = "The Berlin Wall fell on 09/11/1989. 
The first website was launched on 06/08/1991."
Output: Total number of distinct years: 2
Explanation: Two distinct years are referenced: 1989, and 1991

Scenario 2

Input: str = "TutorialsPoint India was founded on 20/08/2006. 
The Java tutorial section was launched on 10/03/2007. 
Major UI revamp was done on 15/01/2021."
Output: Total number of distinct years: 3
Explanation: Three distinct years are referenced: 2006, 2007, and 2021.

Total Number of Distinct Years Using Regex

The following is the algorithm to find the total number of distinct years from a string:

• Initialize the text string that contains dates in the format DD/MM/YYYY.
• Write a regular expression to match dates in the DD/MM/YYYY Format and extract the year part.
• Initialize an empty unordered set to store unique years.
• Use regex to search all date matches in the text and extract the year from each match.
• Add each extracted year to the unordered set.
• Print the size of the unordered set.

Example: Total Number of Distinct Years

In the following C++ example, we use regex to find the total number of distinct years from a string:

#include<iostream>
#include<regex>
#include<unordered_set>
using namespace std;
int uniqueYearsCount(string text) {
   // Step 1: Regex to match DD/MM/YYYY and capture year
   regex date_regex("\\b\\d{2}/\\d{2}/(\\d{4})\\b");
   smatch match;

   unordered_set<string> years;
   while (regex_search(text, match, date_regex)) {
      years.insert(match[1]);
      text = match.suffix();
   }
   return years.size();
}

int main() {
   string text = "TutorialsPoint India was founded on 20/08/2006. The Java tutorial section was launched on 10/03/2007. Major UI revamp was done on 15/01/2021";
   cout << "Total number of distinct years: " << uniqueYearsCount(text) << endl;
   return 0;
}

Following is the output:

Total number of distinct years: 3

What If the Date Format is Different?

Assuming that the date will be in 'DD-MM-YYYY' format and the string will end with a full stop.

Following is the algorithm:

• Traverse the string
• Check if the current character is a digit. Store it in another string.
• Check if the current character is '-', then remove the character stored in another string.
• Check if the length of another string is 4, then it means that is a year.
• Store that year in an unordered_set.
• Return the size of the unordered_set.

Example: Total Number of Distinct Years

Following is another C++ example, to find the number of distinct years if the format is 'DD-MM-YYYY':

#include <bits/stdc++.h>
using namespace std;
int distinctYear(string str)
{
   string anotherStr = "";
   unordered_set<string> uniqueDates;
   for (int i = 0; i < str.length(); i++) {
      if (isdigit(str[i])) {
         anotherStr.push_back(str[i]);
      }
      else if (str[i] == '-') {
         anotherStr.clear();
      }
      else if (anotherStr.length() == 4) {
         uniqueDates.insert(anotherStr);
         anotherStr.clear();
      }
      else{
        anotherStr.clear();
      }
   }
   return uniqueDates.size();
}
int main()
{
   string str = "The Berlin Wall fell on 09/11/1989. The first website was launched on 06/08/1991.";

   cout<<"Total number of distinct years: "<<distinctYear(str);
   return 0;
}

Following is the output:

Total number of distinct years: 2