Problem P76807_en: Sudoku

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

void dibuixa_sudoku(const vector<vector<int> > &sudoku)
{
    cout << endl;
    for (int i = 0; i < 9; i++) {
        cout << sudoku[i][0];
        for (int j = 1; j < 9; j++) {
            cout << " " << sudoku[i][j];
        }
        cout << endl;
    }
}

bool legal(const vector<vector<int> > &sudoku, int f, int c, int n)
{
    //Mirem la fila
    for (int i = 0; i < 9; i++) {
        if (sudoku[i][c] == n) return false;
    }
    //Mirem la columna
    for (int i = 0; i < 9; i++) {
        if (sudoku[f][i] == n) return false;
    }
    //3x3
    int f0 = (f/3)*3, c0 = (c/3)*3;
    for (int i = f0; i < f0 + 3; i++) {
        for (int j = c0; j < c0 + 3; j++) {
            if (sudoku[i][j] == n) return false;
        }
    }
    return true;
}

bool resol_sudoku(vector<vector<int> > &sudoku, int f, int c)
{
    if (f == 9 and c == 0) {
        dibuixa_sudoku(sudoku);
        return true;
    } else {
        if (sudoku[f][c] == 0) {
            for (int i = 1; i <= 9; i++) {
                if (legal(sudoku, f, c, i)) {
                    sudoku[f][c] = i;
                    if (c == 9-1) {
                        if (resol_sudoku(sudoku, f+1, 0)) {
                            return true;
                        }
                    } else {
                        if (resol_sudoku(sudoku, f, c+1)) {
                            return true;
                        }
                    }
                    sudoku[f][c] = 0;
                }
            }
        } else {
            if (c == 9-1) {
                if (resol_sudoku(sudoku, f+1, 0)) {
                    return true;
                }
            } else {
                if (resol_sudoku(sudoku, f, c+1)) {
                    return true;
                }
            }
        }
    }
    return false;
}

int main()
{
    int n;
    cin >> n;
    cout << n << endl;

    for (int i = 0; i < n; i++) {
        //Llegir sudoku
        vector<vector<int> > sudoku(9, vector<int>(9, 0));
        for (int j = 0; j < 9; j++) {
            for (int k = 0; k < 9; k++) {
                char c;
                cin >> c;
                if (c != '.') sudoku[j][k] = int(c - '0');
            }
        }
        resol_sudoku(sudoku, 0, 0);
    }
}