Find All Permutations of an Array using STL in C++

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The permutation of an array refers to a rearrangement of its elements in every possible order. In this article, we will learn how to generate all possible permutation of an array using STL in C++.

The simplest method to find all the permutations of an array is to use next_permutation(). The array has to be sorted in ascending order because this function generate the next lexicographically larger permutation of an array. The below example shows how to implement this method:

#include <bits/stdc++.h>
using namespace std;

int main() {
    int arr[] = {1, 3, 2};
    int n = sizeof(arr) / sizeof(arr[0]);
    sort(arr, arr + n);

    // Generate all permuatation of an array
    do {
        for (int i = 0; i < n; i++)
            cout << arr[i] << " ";
        cout << endl;
    } while (next_permutation(arr, arr + n));
    
    return 0;
}

1 2 3 
1 3 2 
2 1 3 
2 3 1 
3 1 2 
3 2 1 

Explanation: The next_permutation() method returns true if the next permutation exists and rearranges the arr to it and returns false if it doesn't exits. So, we used a loop in the above program that runs till next_permutation() returns false.

Note: This function modifies the given array to generate its next permutation.

Using prev_permutation() Function

The prev_permutation() does just the opposite of the prev_permutation() function and generate all the previous permutation of the given array. But the given array should be sorted in the descending order.

#include <bits/stdc++.h>
using namespace std;

int main() {
    int arr[] = {1, 3, 2};
    int n = sizeof(arr) / sizeof(arr[0]);
    sort(arr, arr + n, greater<int>());

    // Generate all permuatation of an array
    do {
        for (int i = 0; i < n; i++)
            cout << arr[i] << " ";
        cout << endl;
    } while (prev_permutation(arr, arr + n));
    
    return 0;
}

3 2 1 
3 1 2 
2 3 1 
2 1 3 
1 3 2 
1 2 3