perm dans

#include<iostream>
#define NMAX 20
using namespace std;
int n, c1, c2, st[NMAX], used[NMAX];

void display() {
    for (int i = 1; i <= n; i++)
        cout << st[i] << ' ';
    cout << endl;
}

void bktr(int k) {
    if (k == n + 1)
        display();
    else if (k != 2 && k != n - 1) {
        for (int i = 1; i <= n; i++)
            if (!used[i]) {
                used[i] = 1;
                st[k] = i;
                bktr(k + 1);
                used[i] = 0;
            }
    } else
        bktr(k + 1);
}

int main () {
    cin >> n >> c1 >> c2;
    st[2] = c1, st[n - 1] = c2;
    used[c1] = used[c2] = 1;
    bktr(1);
    return 0;
}