All reverse permutations of an array using STL in C++?

In this section we will see how to generate all reverse permutations using the STL in C++. The forward and reverse permutation of some numbers like (1, 2, 3) will be like below −

Forward permutation

1, 2, 3
1, 3, 2
2, 1, 3
2, 3, 1
3, 1, 2
3, 2, 1

Reversed permutation

3, 2, 1
3, 1, 2
2, 3, 1
2, 1, 3
1, 3, 2
1, 2, 3

We will use the previous_permutation() function to get the result

Algorithm

getPermutation(arr, n)

Begin
   sort arr
   reverse the arr
   repeat
      print array elements
   until the previous permutation calculation is not completed
End

Example

 Live Demo

#include<iostream>
#include <algorithm>
using namespace std;
void disp(int arr[], int n){
   for(int i = 0; i<n; i++){
      cout << arr[i] << " ";
   }
   cout << endl;
}
void getPermutation(int arr[], int n) {
   sort(arr, arr + n);
   reverse(arr, arr+n);
   cout << "Possible permutations: \n";
   do{
      disp(arr, n);
   }while(prev_permutation(arr, arr+n));
}
int main() {
   int arr[] = {11, 22, 33, 44};
   int n = sizeof(arr) / sizeof(arr[0]);
   getPermutation(arr, n);
}

Output

Possible permutations:
44 33 22 11
44 33 11 22
44 22 33 11
44 22 11 33
44 11 33 22
44 11 22 33
33 44 22 11
33 44 11 22
33 22 44 11
33 22 11 44
33 11 44 22
33 11 22 44
22 44 33 11
22 44 11 33
22 33 44 11
22 33 11 44
22 11 44 33
22 11 33 44
11 44 33 22
11 44 22 33
11 33 44 22
11 33 22 44
11 22 44 33
11 22 33 44

Arnab Chakraborty

Published on 26-Jul-2019 14:16:03