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# C++ Custom Sort Method for STL Pair Template Program

Hello Everyone!

In this tutorial, we will learn about creating a Custom Sort Method for sorting a Pair Template its implementation using a Vector in the C++ programming language.

To understand the basic functionality of the Pair Template, we will recommend you visit, C++ STL Pair Template, where we have explained this concept in detail from scratch.

For a better understanding of its implementation, refer to the well-commented C++ code given below.

Code:

``````#include <iostream>
#include <bits/stdc++.h>

using namespace std;

//Returns true if x is smaller than y
bool cmp(pair<int, int> x, pair<int, int> y)
{
if (x.first != y.first)
return x.first < y.first; //return the one with smaller first element
else
return x.second < y.second; //if first element is equal then return the one with smaller second element
}

int main()
{
cout << "\n\nWelcome to Studytonight :-)\n\n\n";
cout << " =====  Program to demonstrate Custom Sorting of a Pair Template, in CPP  ===== \n\n";

cout << "\n\nDeclaring a Vector and Filling it with integers.\n\n";

//create an empty vector of pair
vector<pair<int, int>> v;

//insert elements into the vector
v.push_back(make_pair(1, 5));
v.push_back(make_pair(1, 3));
v.push_back(make_pair(2, 6));
v.push_back(make_pair(2, 4));
v.push_back(make_pair(5, 24));

//prining the vector of pairs
cout << "Printing the Vector or Pairs: \n";

int n = v.size();

//Printing the vector
for (int i = 0; i < n; i++)
{
cout << "\nPair is: " << v[i].first << " and " << v[i].second; //accessing the pair elements
}

cout << "\n\n\n--- Calling the Custom Sort Method ---";
//Sorting the vector in ascending order of the pair
sort(v.begin(), v.end(), cmp);

cout << "\n\nThe elements of the Vector after Sorting are:\n ";

//prining the Sorted vector
for (int i = 0; i < n; i++)
{
cout << "\nPair is: " << v[i].first << " and " << v[i].second; //accessing the pair elements
}

cout << "\n\n\n";

return 0;
}``````

Output: We hope that this post helped you develop a better understanding of the concept of the Pair Template and its implementation in CPP. For any query, feel free to reach out to us via the comments section down below.

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