[LeetCode] 529. Minesweeper 扫雷

Let's play the minesweeper game (Wikipedia, online 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.

扫雷游戏，经典的搜索问题。

1. 当点击到雷('M')时，标记为'X'，结束搜索，游戏结束。

2. 当点击到空方块('E')时，如果周围有雷，就计算雷的个数，标记为这个数字，不在搜索。如果周围没有雷的话， 标记为'B'，继续搜索8个挨着的方块。

解法1：DFS

解法2： BFS

Java: DFS

public class Solution {
    public char[][] updateBoard(char[][] board, int[] click) {
        int m = board.length, n = board[0].length;
        int row = click[0], col = click[1];

        if (board[row][col] == 'M') { // Mine
            board[row][col] = 'X';
        }
        else { // Empty
            // Get number of mines first.
            int count = 0;
            for (int i = -1; i < 2; i++) {
                for (int j = -1; j < 2; j++) {
                    if (i == 0 && j == 0) continue;
                    int r = row + i, c = col + j;
                    if (r < 0 || r >= m || c < 0 || c < 0 || c >= n) continue;
                    if (board[r][c] == 'M' || board[r][c] == 'X') count++;
                }
            }

            if (count > 0) { // If it is not a 'B', stop further DFS.
                board[row][col] = (char)(count + '0');
            }
            else { // Continue DFS to adjacent cells.
                board[row][col] = 'B';
                for (int i = -1; i < 2; i++) {
                    for (int j = -1; j < 2; j++) {
                        if (i == 0 && j == 0) continue;
                        int r = row + i, c = col + j;
                        if (r < 0 || r >= m || c < 0 || c < 0 || c >= n) continue;
                        if (board[r][c] == 'E') updateBoard(board, new int[] {r, c});
                    }
                }
            }
        }

        return board;
    }
}

Java: BFS

public class Solution {
    public char[][] updateBoard(char[][] board, int[] click) {
        int m = board.length, n = board[0].length;
        Queue<int[]> queue = new LinkedList<>();
        queue.add(click);

        while (!queue.isEmpty()) {
            int[] cell = queue.poll();
            int row = cell[0], col = cell[1];

            if (board[row][col] == 'M') { // Mine
                board[row][col] = 'X';
            }
            else { // Empty
                // Get number of mines first.
                int count = 0;
                for (int i = -1; i < 2; i++) {
                    for (int j = -1; j < 2; j++) {
                        if (i == 0 && j == 0) continue;
                        int r = row + i, c = col + j;
                        if (r < 0 || r >= m || c < 0 || c < 0 || c >= n) continue;
                        if (board[r][c] == 'M' || board[r][c] == 'X') count++;
                    }
                }

                if (count > 0) { // If it is not a 'B', stop further BFS.
                    board[row][col] = (char)(count + '0');
                }
                else { // Continue BFS to adjacent cells.
                    board[row][col] = 'B';
                    for (int i = -1; i < 2; i++) {
                        for (int j = -1; j < 2; j++) {
                            if (i == 0 && j == 0) continue;
                            int r = row + i, c = col + j;
                            if (r < 0 || r >= m || c < 0 || c < 0 || c >= n) continue;
                            if (board[r][c] == 'E') {
                                queue.add(new int[] {r, c});
                                board[r][c] = 'B'; // Avoid to be added again.
                            }
                        }
                    }
                }
            }
        }

        return board;
    }
}　　

Python:

class Solution(object):
    def updateBoard(self, board, click):
        """
        :type board: List[List[str]]
        :type click: List[int]
        :rtype: List[List[str]]
        """
        q = collections.deque([click])
        while q:
            row, col = q.popleft()
            if board[row][col] == 'M':
                board[row][col] = 'X'
            else:
                count = 0
                for i in xrange(-1, 2):
                    for j in xrange(-1, 2):
                        if i == 0 and j == 0:
                            continue
                        r, c = row + i, col + j
                        if not (0 <= r < len(board)) or not (0 <= c < len(board[r])):
                            continue
                        if board[r][c] == 'M' or board[r][c] == 'X':
                            count += 1

                if count:
                    board[row][col] = chr(count + ord('0'))
                else:
                    board[row][col] = 'B'
                    for i in xrange(-1, 2):
                        for j in xrange(-1, 2):
                            if i == 0 and j == 0:
                                continue
                            r, c = row + i, col + j
                            if not (0 <= r < len(board)) or not (0 <= c < len(board[r])):
                                continue
                            if board[r][c] == 'E':
                                q.append((r, c))
                                board[r][c] = ' '

        return board

Python:

# Time:  O(m * n)
# Space: O(m * n)
class Solution2(object):
    def updateBoard(self, board, click):
        """
        :type board: List[List[str]]
        :type click: List[int]
        :rtype: List[List[str]]
        """
        row, col = click[0], click[1]
        if board[row][col] == 'M':
            board[row][col] = 'X'
        else:
            count = 0
            for i in xrange(-1, 2):
                for j in xrange(-1, 2):
                    if i == 0 and j == 0:
                        continue
                    r, c = row + i, col + j
                    if not (0 <= r < len(board)) or not (0 <= c < len(board[r])):
                        continue
                    if board[r][c] == 'M' or board[r][c] == 'X':
                        count += 1

            if count:
                board[row][col] = chr(count + ord('0'))
            else:
                board[row][col] = 'B'
                for i in xrange(-1, 2):
                    for j in xrange(-1, 2):
                        if i == 0 and j == 0:
                            continue
                        r, c = row + i, col + j
                        if not (0 <= r < len(board)) or not (0 <= c < len(board[r])):
                            continue
                        if board[r][c] == 'E':
                            self.updateBoard(board, (r, c))

        return board

C++:

// Time:  O(m * n)
// Space: O(m + n)

class Solution {
public:
    vector<vector<char>> updateBoard(vector<vector<char>>& board, vector<int>& click)  {
        queue<vector<int>> q;
        q.emplace(click);
        while (!q.empty()) {
            int row = q.front()[0], col = q.front()[1];
            q.pop();
            if (board[row][col] == 'M') {
                board[row][col] = 'X';
            } else {
                int count = 0;
                for (int i = -1; i < 2; ++i) {
                    for (int j = -1; j < 2; ++j) {
                        if (i == 0 && j == 0) {
                            continue;
                        }
                        int r = row + i, c = col + j;
                        if (r < 0 || r >= board.size() || c < 0 || c < 0 || c >= board[r].size()) {
                            continue;
                        }
                        if (board[r][c] == 'M' || board[r][c] == 'X') {
                            ++count;
                        }
                    }
                }

                if (count > 0) {
                    board[row][col] = count + '0';
                } else {
                    board[row][col] = 'B';
                    for (int i = -1; i < 2; ++i) {
                        for (int j = -1; j < 2; ++j) {
                            if (i == 0 && j == 0) {
                                continue;
                            }
                            int r = row + i, c = col + j;
                            if (r < 0 || r >= board.size() || c < 0 || c < 0 || c >= board[r].size()) {
                                continue;
                            }
                            if (board[r][c] == 'E') {
                                vector<int> next_click = {r, c};
                                q.emplace(next_click);
                                board[r][c] = 'B';
                            }
                        }
                    }
                }
            }
        }

        return board;
    }
};

C++:

// Time:  O(m * n)
// Space: O(m * n)
class Solution2 {
public:
    vector<vector<char>> updateBoard(vector<vector<char>>& board, vector<int>& click)  {
        int row = click[0], col = click[1];
        if (board[row][col] == 'M') {
            board[row][col] = 'X';
        } else {
            int count = 0;
            for (int i = -1; i < 2; ++i) {
                for (int j = -1; j < 2; ++j) {
                    if (i == 0 && j == 0) {
                        continue;
                    }
                    int r = row + i, c = col + j;
                    if (r < 0 || r >= board.size() || c < 0 || c < 0 || c >= board[r].size()) {
                        continue;
                    }
                    if (board[r][c] == 'M' || board[r][c] == 'X') {
                        ++count;
                    }
                }
            }

            if (count > 0) {
                board[row][col] = count + '0';
            } else {
                board[row][col] = 'B';
                for (int i = -1; i < 2; ++i) {
                    for (int j = -1; j < 2; ++j) {
                        if (i == 0 && j == 0) {
                            continue;
                        }
                        int r = row + i, c = col + j;
                        if (r < 0 || r >= board.size() || c < 0 || c < 0 || c >= board[r].size()) {
                            continue;
                        }
                        if (board[r][c] == 'E') {
                            vector<int> next_click = {r, c};
                            updateBoard(board, next_click);
                        }
                    }
                }
            }
        }

        return board;
    }
};

　　

　　

　　

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