leetcode 37 Sudoku Solver

class Solution {public:     typedef vector<vector<char> >::size_type sz;    typedef set<char>::iterator Sit;    void solveSudoku(vector<vector<char>>& board) {        sz size = board.size();        // initialize the flags        set<char> tmp;        for(int i = 1; i < 10; ++i) {            tmp.insert('0' + i);        }        rflag = vector<set<char> >(size, tmp);        cflag = vector<set<char> >(size, tmp);        bflag = vector<set<char> >(size, tmp);        for (sz i = 0; i < size; ++i) {            for (sz j = 0; j < size; ++j) {                char ch = board[i][j];                if (ch != '.') {                    rflag[i].erase(ch);                    cflag[j].erase(ch);                    bflag[j / 3 * 3 + i / 3].erase(ch);                }            }        }        solve(board, 0);        return;    }private:    // mark every row    vector<set<char> > rflag;    // mark every column    vector<set<char> > cflag;    // mark every box    vector<set<char> > bflag;    bool solve(vector<vector<char>>& board, sz ir) {        sz size = board.size();         for (sz i = ir; i < size; ++i) {            for (sz j = 0; j < size; ++j){                char ch = board[i][j];                if (ch == '.') {                    set<char> vals(rflag[i]);                    for (Sit it = vals.begin(); it != vals.end();) {                        if (cflag[j].find(*it) == cflag[j].end()                             || bflag[j / 3 * 3 + i / 3].find(*it) == bflag[j / 3 * 3 + i / 3].end()){ // 取共有元素                            vals.erase(*it++);                        } else                            ++it;                    }                    if (vals.empty()) {                        return false;                    }                    for (Sit it = vals.begin(); it != vals.end(); ++it) {                                board[i][j] = *it;                        rflag[i].erase(*it);                        cflag[j].erase(*it);                        bflag[j / 3 * 3 + i / 3].erase(*it);                        if (solve(board, i) == false) {                            rflag[i].insert(*it);                            cflag[j].insert(*it);                            bflag[j / 3 * 3 + i / 3].insert(*it);                        } else {                            return true;                        }                    }                    board[i][j] = '.'; // 标回去                    return false;                }            }        }        return true;    // end    }};

参考后

class Solution {public:    void solveSudoku(vector<vector<char>>& board) {        solve(board, 0);    }private:    bool solve(vector<vector<char> >& board, size_t r) {        size_t size = board.size();        for (size_t i = r; i < size; ++i) {            for (size_t j = 0; j < size; ++j) {                char ch = board[i][j];                if (ch == '.') {                    for (int k = 1; k <= 9; ++k) {                        char val = '0' + k;                        if (isValid(board, i, j, val)) {                            board[i][j] = val;                            if (solve(board, i) == true)                                 return true;                        }                    }                    board[i][j] = '.';                    return false;                }            }        }        return true; // fill all the empty, all the solve is end    }    bool isValid(vector<vector<char> >& board, size_t row, size_t col, char c) {        size_t size = board.size();        size_t val = 'c' - '0';        for (size_t i = 0; i < size; ++i) {            // check row            // check column            // check block            if (board[i][col] == c || board[row][i] == c ||                 board[(row / 3 * 3 + col / 3) / 3  * 3 + i / 3][(row / 3 * 3 + col / 3) % 3 * 3 + i % 3] == c)                return false;        }        return true;      }};