# Minesweeper Problem

## Description

LeetCode Problem 529.

Let’s play the minesweeper game !

You are given an m x n char matrix board representing the game board where:

- ‘M’ represents an unrevealed mine,
- ‘E’ represents an unrevealed empty square,
- ‘B’ represents a revealed blank square that has no adjacent mines (i.e., above, below, left, right, and all 4 diagonals),
- digit (‘1’ to ‘8’) represents how many mines are adjacent to this revealed square, and
- ‘X’ represents a revealed mine.

You are also given an integer array click where click = [click_r, click_c] represents the next click position among all the unrevealed squares (‘M’ or ‘E’).

Return the board after revealing this position according to the following rules:

- If a mine ‘M’ is revealed, then the game is over. You should change it to ‘X’.
- If an empty square ‘E’ with no adjacent mines is revealed, then change it to a revealed blank ‘B’ and all of its adjacent unrevealed squares should be revealed recursively.
- 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.
- Return the board when no more squares will be revealed.

Example 1:

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Input: board = [["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"]]

Example 2:

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Input: board = [["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"]]

Constraints:

- m == board.length
- n == board[i].length
- 1 <= m, n <= 50
- board[i][j] is either ‘M’, ‘E’, ‘B’, or a digit from ‘1’ to ‘8’.
- click.length == 2
- 0 <= click_r < m
- 0 <= click_c < n
- board[click_r][click_c] is either ‘M’ or ‘E’.

## Sample C++ Code using Depth-First Search

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class Solution {
public:
int dx[8] = {-1, 0, 1, 0, -1, -1, 1, 1};
int dy[8] = {0, 1, 0, -1, -1, 1, 1, -1};
bool isValid(vector<vector<char>>& board, int i, int j) {
return (i >= 0 && j >= 0 && i < board.size() && j < board[0].size());
}
int hasAdjacentMine(vector<vector<char>>& board, int i, int j) {
int count = 0;
for (int k=0; k<8; k++) {
int I = i + dx[k];
int J = j + dy[k];
if (isValid(board, I, J) && board[I][J] == 'M')
count++;
}
return count;
}
void dfs(vector<vector<char>>& board, vector<vector<bool>>& visited, int i, int j) {
if (min(i, j) < 0 || i >= board.size() || j >= board[0].size() || visited[i][j]) return;
visited[i][j] = true;
if (board[i][j] == 'M') {
board[i][j] = 'X';
return;
}
if (board[i][j] == 'E') {
int c = hasAdjacentMine(board, i, j);
if (c == 0) {
board[i][j] = 'B';
for (int k=0; k<8; k++) {
dfs(board, visited, i+dx[k], j+dy[k]);
}
}
else {
board[i][j] = c + '0';
return;
}
}
}
vector<vector<char>> updateBoard(vector<vector<char>>& board, vector<int>& click) {
vector<vector<bool>> visited(board.size(), vector<bool>(board[0].size(), false));
dfs(board, visited, click[0], click[1]);
return board;
}
};