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How to reverse a Vector using STL in C++?

  • Difficulty Level : Basic
  • Last Updated : 30 May, 2021
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Given a vector, reverse this vector using STL in C++.
Example: 
 

Input: vec = {1, 45, 54, 71, 76, 12}
Output: {12, 76, 71, 54, 45, 1}

Input: vec = {1, 7, 5, 4, 6, 12}
Output: {12, 6, 4, 5, 7, 1}

Approach: Reversing can be done with the help of reverse() function provided in STL. The Time complexity of the reverse() is O(n) where n is the length of the string.
Syntax: 

reverse(start_index, last_index);

CPP




// C++ program to reverse Vector
// using reverse() in STL
 
#include <bits/stdc++.h>
using namespace std;
 
int main()
{
 
    // Get the vector
    vector<int> a = { 1, 45, 54, 71, 76, 12 };
 
    // Print the vector
    cout << "Vector: ";
    for (int i = 0; i < a.size(); i++)
        cout << a[i] << " ";
    cout << endl;
 
    // Reverse the vector
    reverse(a.begin(), a.end());
 
    // Print the reversed vector
    cout << "Reversed Vector: ";
    for (int i = 0; i < a.size(); i++)
        cout << a[i] << " ";
    cout << endl;
 
    return 0;
}
Output: 
Vector: 1 45 54 71 76 12 
Reversed Vector: 12 76 71 54 45 1

 

Time Complexity: O(n) where n is the length of the string.

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