LEETCODE 37. Sudoku Solver

题目大意

是leetcode36的进阶版，要解出数独的答案

解题思路

就是用递归，无奈太渣，弄错了边界条件，而且思路还不够清晰，递归函数返回类型一开始写成void了，导致board里面的内容总是被清空，后来改成bool，并在清空内容之前做一下判断。

实现代码

class Solution {
public:
    void solveSudoku(vector<vector<char>>& board) {
        bool rowFlag[9][9] = {false}, colFlag[9][9] = {false}, blockFlag[9][9] = {false};
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                if (board[i][j] != '.') {
                    rowFlag[board[i][j] - '1'][i] = true;
                    colFlag[board[i][j] - '1'][j] = true;
                    blockFlag[board[i][j] - '1'][i / 3 * 3 + j / 3] = true;
                }
            }
        }
        recursion(board, rowFlag, colFlag, blockFlag, 0, 0);
    }
private:
    bool recursion(vector<vector<char>>& board, bool rowFlag[9][9], bool colFlag[9][9], bool blockFlag[9][9], int row, int col) {
        if (row == 9 && col == 0) {
            return true;
        }
        if (board[row][col] != '.') {
            col++;
            if (col > 8) {
                col = 0;
                row++;
            }
            return recursion(board, rowFlag, colFlag, blockFlag, row, col);
        } else {
            for (int i = 1; i <= 9; i++) {
                if (!rowFlag[i - 1][row] && !colFlag[i - 1][col] && !blockFlag[i - 1][row / 3 * 3 + col / 3]) {
                    rowFlag[i - 1][row] = true;
                    colFlag[i - 1][col] = true;
                    blockFlag[i - 1][row / 3 * 3 + col / 3] = true;
                    board[row][col] = i + '0';
                    int newRow = row, newCol = col + 1;
                    if (newCol > 8) {
                        newCol = 0;
                        newRow++;
                    }
                    bool flag = recursion(board, rowFlag, colFlag, blockFlag, newRow, newCol);
                    if (!flag) {
                        rowFlag[i - 1][row] = false;
                        colFlag[i - 1][col] = false;
                        blockFlag[i - 1][row / 3 * 3 + col / 3] = false;
                        board[row][col] = '.';
                    } else {
                        return true;
                    }
                }
            }
            return false;
        }
    }
};