Problem P17921_ca: Reines (2)

#include <iostream>
#include <vector>
#include <cmath>
using namespace std;


void escriure_tauler(const vector<int> &sp, int n)
{
    vector<vector<char> > m(n, vector<char>(n, '.'));

    for (int i = 0; i < n; i++) {
        m[sp[i]][i] = 'Q';
        for (int j = 0; j < n; j++) {
            cout << m[j][i];
        }
        cout << endl;
    }
    cout << endl;
}

bool legal(const vector<int> &sp, int q, int n, int y,
    const vector<bool> &fila,
    const vector<bool> &diag_pos,
    const vector<bool> &diag_neg)
{
    return not (fila[y] or diag_pos[q+y] or diag_neg[(n-y)+q-1]);
}

void reines(vector<int> &sp, int q, int n,
    vector<bool> &fila,
    vector<bool> &diag_pos,
    vector<bool> &diag_neg)
{
    if (q == n) escriure_tauler(sp, n);
    else {
        for (int y = 0; y < n; y++) {
            if (legal(sp, q, n, y, fila, diag_pos, diag_neg)) {
                sp[q] = y;
                fila[y] = true;
                diag_pos[q+y] = true;
                diag_neg[(n-y)+q-1] = true;
                reines(sp, q+1, n, fila, diag_pos, diag_neg);
                diag_neg[(n-y)+q-1] = false;
                diag_pos[q+y] = false;
                fila[y] = false;
                sp[q] = -1;
            }
        }
    }
}

int main()
{
    int n;
    cin >> n;
    vector<bool> fila(n, false),
        diag_neg(2*n-1, false),
        diag_pos(2*n-1, false);
    vector<int> sp(n, -1);
    reines(sp, 0, n, fila, diag_pos, diag_neg);
}