随手练——数独 HDU - 5547 坑！坑！坑！

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

int M[4][4];
bool flag = false;

int check(int row, int column, int x) {
    for (int i = 0; i < 4; i++) {
        if (M[i][column] == x || M[row][i] == x)
            return 0;
    }
    int r = row / 2 * 2, c = column / 2 * 2;
    for (int i = r; i < r + 2; i++) {
        for (int j = c; j < c + 2; j++) {
            if (M[i][j] == x) return 0;
        }
    }
    return 1;
}


void DFS(int row, int column) {
    if (row == 4) {
        flag = true;
        return;
    }

    if (M[row][column] == -6) {
        int i;
        for (i = 1; i <= 4; i++) {
            if (check(row, column, i)) {
                M[row][column] = i;
                DFS(row + (column + 1) / 4, (column + 1) % 4);
                if (flag) return;    
            }
        }
        if (i == 5) {
            M[row][column] = -6;
            return;
        }
    }
    DFS(row + (column + 1) / 4, (column + 1) % 4);
}
int main() {
    int i = 1,n;
    cin >> n;    string s;
    cin.ignore();
    while (n--) {
        flag = false;
        for (int i = 0; i < 4; i++) {
            getline(cin, s);
            if (s.empty()) {
                i--;
                continue;
            }
            for (int j = 0; j < 4; j++) {
                M[i][j] = s[j]-‘0‘;
            }
        }
        DFS(0, 0);
        cout << "Case #" << i++ << ":" << endl;
        for (int i = 0; i < 4; i++) {
            for (int j = 0; j < 4; j++) {
                cout << M[i][j];
            }
            cout << endl;
        }
    }
    return 0;
}