Heap's algorithm is an algorithm used for generating all possible permutations of some given length.

HeapPermute.cpp

#include <iostream>

using namespace std;

const int SIZE = 4;

void printArray(int arr[], int size) 
{
    for ( int i = 0; i < size; i++ )
        cout << arr[i] << ' ';
    cout << endl;
}

void permute(int v[], int n) 
{
    if (n == 1) {
        printArray(v, SIZE);
    } else {
        for (int i = 0; i < n; i++) {
            permute(v, n-1);
            if (n % 2 == 1) {
                swap(v[0], v[n-1]);
            } else {
                swap(v[i], v[n-1]);
            }
        }
    }
}

int main() 
{
    int ns[] = {1, 2, 3, 4};
    permute(ns, SIZE);
}