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How to join two Vectors using STL in C++?
  • Difficulty Level : Basic
  • Last Updated : 28 May, 2021

Given two vectors, join these two vectors using STL in C++.
Example: 
 

Input: 
vec1 = {1, 45, 54, 71, 76, 12}, 
vec2 = {1, 7, 5, 4, 6, 12} 
Output: {1, 4, 5, 6, 7, 12, 45, 54, 71, 76}
Input: 
vec1 = {1, 7, 5, 4, 6, 12}, 
vec2 = {10, 12, 11} 
Output: {1, 4, 5, 6, 7, 10, 11, 12} 
 

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Approach: Joining can be done with the help of set_union() function provided in STL.
Syntax:  

set_union (InputIterator1 first1, InputIterator1 last1,
           InputIterator2 first2, InputIterator2 last2,
           OutputIterator result);

CPP




// C++ program to join two Vectors
// using set_union() in STL
 
#include <bits/stdc++.h>
using namespace std;
 
int main()
{
    // Get the vector
    vector<int> vector1 = { 1, 45, 54, 71, 76, 12 };
    vector<int> vector2 = { 1, 7, 5, 4, 6, 12 };
 
    // Sort the vector
    sort(vector1.begin(), vector1.end());
    sort(vector2.begin(), vector2.end());
 
    // Print the vector
    cout << "First Vector: ";
    for (int i = 0; i < vector1.size(); i++)
        cout << vector1[i] << " ";
    cout << endl;
 
    cout << "Second Vector: ";
    for (int i = 0; i < vector2.size(); i++)
        cout << vector2[i] << " ";
    cout << endl;
 
    // Initialise a vector
    // to store the common values
    // and an iterator
    // to traverse this vector
    vector<int> v(vector1.size() + vector2.size());
    vector<int>::iterator it, st;
 
    it = set_union(vector1.begin(),
                   vector1.end(),
                   vector2.begin(),
                   vector2.end(),
                   v.begin());
 
    cout << "\nAfter joining:\n";
    for (st = v.begin(); st != it; ++st)
        cout << *st << ", ";
    cout << '\n';
 
    return 0;
}
Output: 
First Vector: 1 12 45 54 71 76 
Second Vector: 1 4 5 6 7 12 

After joining:
1, 4, 5, 6, 7, 12, 45, 54, 71, 76,

 

Note that the vector should not contain 1 element twice:

In case you enter same elements, the set_union function will only consider 1 instance of the element, and default rest to 0.

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