LN : leetcode 529 Minesweeper

lc 529 Minesweeper

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529 Minesweeper

Let's play the minesweeper game!

You are given a 2D char matrix representing the game board. 'M' represents an unrevealed mine, 'E' represents an unrevealed empty square, 'B' represents a revealed blank square that has no adjacent (above, below, left, right, and all 4 diagonals) mines, digit ('1' to '8') represents how many mines are adjacent to this revealed square, and finally 'X' represents a revealed mine.

Now given the next click position (row and column indices) among all the unrevealed squares ('M' or 'E'), return the board after revealing this position according to the following rules:

1. If a mine ('M') is revealed, then the game is over - change it to
   'X'.
2. If an empty square ('E') with no adjacent mines is revealed, then
   change it to revealed blank ('B') and all of its adjacent unrevealed
   squares should be revealed recursively.
3. If an empty square ('E') with at least one adjacent mine is
   revealed, then change it to a digit ('1' to '8') representing the
   number of adjacent mines.
4. Return the board when no more squares will be revealed.

Example 1:

Input: 

[['E', 'E', 'E', 'E', 'E'],
 ['E', 'E', 'M', 'E', 'E'],
 ['E', 'E', 'E', 'E', 'E'],
 ['E', 'E', 'E', 'E', 'E']]

Click : [3,0]

Output: 

[['B', '1', 'E', '1', 'B'],
 ['B', '1', 'M', '1', 'B'],
 ['B', '1', '1', '1', 'B'],
 ['B', 'B', 'B', 'B', 'B']]

Explanation:

Example 2:

Input: 

[['B', '1', 'E', '1', 'B'],
 ['B', '1', 'M', '1', 'B'],
 ['B', '1', '1', '1', 'B'],
 ['B', 'B', 'B', 'B', 'B']]

Click : [1,2]

Output: 

[['B', '1', 'E', '1', 'B'],
 ['B', '1', 'X', '1', 'B'],
 ['B', '1', '1', '1', 'B'],
 ['B', 'B', 'B', 'B', 'B']]

Explanation:

Note:

1. The range of the input matrix's height and width is [1,50].
2. The click position will only be an unrevealed square ('M' or 'E'),
   which also means the input board contains at least one clickable
   square.
3. The input board won't be a stage when game is over (some mines have
   been revealed).
4. For simplicity, not mentioned rules should be ignored in this
   problem.For example, you don't need to reveal all the unrevealed
   mines when the game is over, consider any cases that you will win
   the game or flag any squares.

递归 Accepted##

扫雷游戏，其实还挺简单的，注意判断是否在版图之内，利用递归不断推算并且更新。

class Solution {
public:
    vector<vector<char>> updateBoard(vector<vector<char>>& board, vector<int>& click) {
        if (board[click[0]][click[1]] == 'M') {
            board[click[0]][click[1]] = 'X';
            return board;
        }
        reveal(board, click[0], click[1]);
        return board;
    }
    
    int out(vector<vector<char>>& board, int x, int y) {
        return (x < 0 || y < 0 || x >= board.size() || y >= board[0].size());
    }
    
    void reveal(vector<vector<char>>& board, int x, int y) {
        if (out(board, x, y))   return;
        if (board[x][y] == 'E') {
            int m = 0;
            if (!out(board, x-1, y-1) && board[x-1][y-1] == 'M') m++;
            if (!out(board, x-1, y) && board[x-1][y] == 'M') m++;
            if (!out(board, x-1, y+1) && board[x-1][y+1] == 'M') m++;
            if (!out(board, x, y-1) && board[x][y-1] == 'M') m++;
            if (!out(board, x, y+1) && board[x][y+1] == 'M') m++;
            if (!out(board, x+1, y-1) && board[x+1][y-1] == 'M') m++;
            if (!out(board, x+1, y+1) && board[x+1][y+1] == 'M') m++;
            if (!out(board, x+1, y) && board[x+1][y] == 'M') m++;
            if (m) {
                board[x][y] = '0'+m;
            } else {
                board[x][y] = 'B';
                reveal(board, x-1, y-1);
                reveal(board, x-1, y);
                reveal(board, x-1, y+1);
                reveal(board, x, y-1);
                reveal(board, x, y+1);
                reveal(board, x+1, y-1);
                reveal(board, x+1, y+1);
                reveal(board, x+1, y);
            }
        }
    }
};