All reverse permutations of an array using STL in C++
Last Updated :
01 Apr, 2019
Given an array, the task is to print or display all the reverse permutations of this array using STL in C++. Reverse permutation means, for an array {1, 2, 3}:
forward permutations:
1 2 3
1 3 2
2 1 3
2 3 1
3 1 2
3 2 1
reverse permutations:
3 2 1
3 1 2
2 3 1
2 1 3
1 3 2
1 2 3
Examples:
Input: a[] = {1, 2, 3}
Output:
3 2 1
3 1 2
2 3 1
2 1 3
1 3 2
1 2 3
Input: a[] = {10, 20, 30, 40}
Output:
Possible permutations are:
40 30 20 10
40 30 10 20
40 20 30 10
40 20 10 30
40 10 30 20
40 10 20 30
30 40 20 10
30 40 10 20
30 20 40 10
30 20 10 40
30 10 40 20
30 10 20 40
20 40 30 10
20 40 10 30
20 30 40 10
20 30 10 40
20 10 40 30
20 10 30 40
10 40 30 20
10 40 20 30
10 30 40 20
10 30 20 40
10 20 40 30
10 20 30 40
Approach: The next possible permutation of the array in reverse order can be found using prev_permutation() function provided in STL.
Syntax:
bool prev_permutation (BidirectionalIterator first,
BidirectionalIterator last);
Below is the implementation of the above Approach:
#include <bits/stdc++.h>
using namespace std;
void display( int a[], int n)
{
for ( int i = 0; i < n; i++) {
cout << a[i] << " " ;
}
cout << endl;
}
void findPermutations( int a[], int n)
{
sort(a, a + n);
reverse(a, a + n);
cout << "Possible permutations are:\n" ;
do {
display(a, n);
} while (prev_permutation(a, a + n));
}
int main()
{
int a[] = { 10, 20, 30, 40 };
int n = sizeof (a) / sizeof (a[0]);
findPermutations(a, n);
return 0;
}
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Output:
Possible permutations are:
40 30 20 10
40 30 10 20
40 20 30 10
40 20 10 30
40 10 30 20
40 10 20 30
30 40 20 10
30 40 10 20
30 20 40 10
30 20 10 40
30 10 40 20
30 10 20 40
20 40 30 10
20 40 10 30
20 30 40 10
20 30 10 40
20 10 40 30
20 10 30 40
10 40 30 20
10 40 20 30
10 30 40 20
10 30 20 40
10 20 40 30
10 20 30 40
Related Article: All permutations of an array using STL in C++
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