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How to traverse a C++ set in reverse direction

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  • Last Updated : 07 Aug, 2022
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Given a Set, the task is to traverse this Set in reverse order. Examples:

Input: set = [10 20 30 70 80 90 100 40 50 60]
Output: 100 90 80 70 60 50 40 30 20 10 

Input: set = [1 2 3 4 5]
Output: 5 4 3 2 1

Approach: To traverse a Set in reverse order, a reverse_iterator can be declared on it and it can be used to traverse the set from the last element to the first element with the help of rbegin() and rend() functions.

  1. Get the set.
  2. Declare the reverse iterator on this set.
  3. Traverse the set from the last element to the first element with the help of rbegin() and rend() functions.

Below is the implementation of the above approach: Program: 

CPP




#include <bits/stdc++.h>
using namespace std;
 
int main()
{
 
    // Get the set
    int arr[] = { 14, 12, 15, 11, 10 };
 
    // initializes the set from an array
    set<int> s(arr, arr + sizeof(arr) / sizeof(arr[0]));
 
    // declare iterator on set
    set<int>::iterator it;
 
    cout << "Elements of Set in normal order:\n";
 
    // prints all elements in normal order
    // using begin() and end() methods
    for (it = s.begin(); it != s.end(); it++)
        cout << *it << " ";
 
    // declare reverse_iterator on set
    set<int>::reverse_iterator rit;
 
    cout << "\nElements of Set in reverse order:\n";
 
    // prints all elements in reverse order
    // using rbegin() and rend() methods
    for (rit = s.rbegin(); rit != s.rend(); rit++)
        cout << *rit << " ";
 
    return 0;
}

Output:

Elements of Set in normal order:
10 11 12 14 15 
Elements of Set in reverse order:
15 14 12 11 10

Time complexity: O(n) where n is no of elements in the given set

Auxiliary Space: O(n)

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