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 −
1, 2, 3 1, 3, 2 2, 1, 3 2, 3, 1 3, 1, 2 3, 2, 1
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
Begin sort arr reverse the arr repeat print array elements until the previous permutation calculation is not completed End
#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); }
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