Answer to Question #321219 in C++ for Christian

Question

A code is required to print all possible arrangement of combination of an array(of 'k' elements), i.e. the permutation of the result of combination.

Let's say the array has the following elements (k=4):

"alpha", "beta", "gamma", "delta".

Then, we choose r=3

The expected result is as follows:

alpha beta gamma

alpha gamma beta

beta alpha gamma

beta gamma alpha

gamma alpha beta

gamma beta alpha

alpha beta delta

alpha delta beta

beta alpha delta

beta delta alpha

delta alpha beta

delta beta alpha

alpha delta gamma

alpha gamma delta

delta alpha gamma

delta gamma alpha

gamma alpha delta

gamma delta alpha

beta delta gamma

beta gamma delta

delta beta gamma

delta gamma beta

gamma beta delta

gamma delta beta

From the above result above, all unique PERMUTATION of the COMBINATION of r=3 from the array of k=4 elements is completed.

This is confirmed since 4C3 x 3! = 24 lines of results

Answer 1

#include <iostream>
#include <vector>
#include <string>


using namespace std;


void print_permutation(vector<string>& from, int r, vector<string>& perm) {
    if (r == 0) {
        for (size_t i=0; i<perm.size(); i++) {
            cout << perm[i] << " ";
        }
        cout << endl;
        return;
    }

    for (auto it=from.begin(); it!=from.end(); ++it) {
        perm.push_back(*it);
        vector<string> v;
        v.insert(v.begin(), from.begin(), it);
        v.insert(v.end(), it+1, from.end());
        print_permutation(v, r-1, perm);
        perm.pop_back();
    }
}

int main() {
    vector<string> v = {"alpha", "beta", "gamma", "delta"};
    vector<string> perm;

    print_permutation(v, 3, perm);

    return 0;
}