解数独 【笔试题】

本题虽然是困难 但是难度不大 写的时候也是有经验

class Solution {
    public void solveSudoku(char[][] board) {
        backtrack(board,0,0);

    }

    public boolean backtrack(char[][] board, int i, int j){
        int m = 9, n = 9;
        if(j == n){
            return backtrack(board, i+1, 0);
        }
        if(i == m){
            return true;
        }
        if(board[i][j] != '.'){
            return backtrack(board, i, j+1);
        }

        for(char ch = '1'; ch <= '9'; ch++){
            if(!isValid(board,i,j,ch)){
                continue;
            }

            board[i][j] = ch;

            if(backtrack(board, i, j+1)){
                return true;
            }
            board[i][j] = '.';
        }
        return false;
    }

//判断是否有效
    public boolean isValid(char[][] board, int r, int c, char n){
        for(int i = 0; i < 9; i++){
            if(board[r][i] == n){
                return false;
            }
            if(board[i][c] == n){
                return false;
            }
            if(board[(r/3) * 3 + (i / 3)][(c/3) * 3 + (i%3)] == n ){
                return false;
            }
        }
        return true;
    }
}