Solution.cpp

using pii = pair<int, int>;

class Solution {
public:
    void solveSudoku(vector<vector<char>>& board) {
        bool row[9][9] = {false};
        bool col[9][9] = {false};
        bool block[3][3][9] = {false};
        bool ok = false;
        vector<pii> t;
        for (int i = 0; i < 9; ++i) {
            for (int j = 0; j < 9; ++j) {
                if (board[i][j] == '.') {
                    t.push_back({i, j});
                } else {
                    int v = board[i][j] - '1';
                    row[i][v] = col[j][v] = block[i / 3][j / 3][v] = true;
                }
            }
        }
        function<void(int k)> dfs = [&](int k) {
            if (k == t.size()) {
                ok = true;
                return;
            }
            int i = t[k].first, j = t[k].second;
            for (int v = 0; v < 9; ++v) {
                if (!row[i][v] && !col[j][v] && !block[i / 3][j / 3][v]) {
                    row[i][v] = col[j][v] = block[i / 3][j / 3][v] = true;
                    board[i][j] = v + '1';
                    dfs(k + 1);
                    row[i][v] = col[j][v] = block[i / 3][j / 3][v] = false;
                }
                if (ok) {
                    return;
                }
            }
        };
        dfs(0);
    }
};