37_数独

class Solution {
    public void solveSudoku(char[][] board) {
        //最骚的一点：给递归函数一个返回值 直接调用 太帅了
        bp(board);
    }
    private boolean bp(char[][] board){
        for(int i =0;i<9;i++){
            for(int j =0; j<9 ;j++){
                if(board[i][j] != '.') continue;
                for(char z = '1';z<='9';z++){
                    if(isValid(i,j,z,board)){
                        //进入递归
                        board[i][j] = z;
                        if(bp(board)) return true;
                        board[i][j] = '.';
                    }
                }
                return false;
            }
            
        }
        return true;
    }
    private boolean isValid(int r,int c,char v,char[][] board){
        for(int i =0;i<9;i++){
            if(board[r][i] == v) return false;
            if(board[i][c] == v) return false;
        }
        int i = (r/3)*3;
        int j = (c/3)*3;
        for(int a = i;a<i+3;a++){
            for(int b = j;b<j+3;b++){
                if(board[a][b] == v) return false;
            }
        }
        return true;
    }
}