<p>You are given an <code>m x n</code> matrix <code>board</code> containing <strong>letters</strong> <code>&#39;X&#39;</code> and <code>&#39;O&#39;</code>, <strong>capture regions</strong> that are <strong>surrounded</strong>:</p>

<ul>
	<li><strong>Connect</strong>: A cell is connected to adjacent cells horizontally or vertically.</li>
	<li><strong>Region</strong>: To form a region <strong>connect every</strong> <code>&#39;O&#39;</code> cell.</li>
	<li><strong>Surround</strong>: The region is surrounded with <code>&#39;X&#39;</code> cells if you can <strong>connect the region </strong>with <code>&#39;X&#39;</code> cells and none of the region cells are on the edge of the <code>board</code>.</li>
</ul>

<p>A <strong>surrounded region is captured</strong> by replacing all <code>&#39;O&#39;</code>s with <code>&#39;X&#39;</code>s in the input matrix <code>board</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">board = [[&quot;X&quot;,&quot;X&quot;,&quot;X&quot;,&quot;X&quot;],[&quot;X&quot;,&quot;O&quot;,&quot;O&quot;,&quot;X&quot;],[&quot;X&quot;,&quot;X&quot;,&quot;O&quot;,&quot;X&quot;],[&quot;X&quot;,&quot;O&quot;,&quot;X&quot;,&quot;X&quot;]]</span></p>

<p><strong>Output:</strong> <span class="example-io">[[&quot;X&quot;,&quot;X&quot;,&quot;X&quot;,&quot;X&quot;],[&quot;X&quot;,&quot;X&quot;,&quot;X&quot;,&quot;X&quot;],[&quot;X&quot;,&quot;X&quot;,&quot;X&quot;,&quot;X&quot;],[&quot;X&quot;,&quot;O&quot;,&quot;X&quot;,&quot;X&quot;]]</span></p>

<p><strong>Explanation:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/02/19/xogrid.jpg" style="width: 367px; height: 158px;" />
<p>In the above diagram, the bottom region is not captured because it is on the edge of the board and cannot be surrounded.</p>
</div>

<p><strong class="example">Example 2:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">board = [[&quot;X&quot;]]</span></p>

<p><strong>Output:</strong> <span class="example-io">[[&quot;X&quot;]]</span></p>
</div>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>m == board.length</code></li>
	<li><code>n == board[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 200</code></li>
	<li><code>board[i][j]</code> is <code>&#39;X&#39;</code> or <code>&#39;O&#39;</code>.</li>
</ul>

class Solution:

    def bfs_capture(self, board, seen, point):
        if point in seen:
            return
        r, c = point

        if r == -1:
            return
        if r == len(board):
            return
        if c == -1:
            return
        if c == len(board[0]):
            return

        if board[r][c] == 'X':
            return 

        board[r][c] = 'X'
        seen.add(point)

        self.bfs_capture(board, seen, (r+1, c))
        self.bfs_capture(board, seen, (r-1, c))
        self.bfs_capture(board, seen, (r, c+1))
        self.bfs_capture(board, seen, (r, c-1))

    def bfs_is_edge(self, board, potential_starting_points, seen, point):
        print(point)
        if point in seen:
            return False
        r, c = point

        if board[r][c] == 'X':
            return False

        seen.add(point)
        potential_starting_points.discard(point)

        is_edge = (r == 0) or (r == len(board) - 1) or (c == 0) or (c == len(board[0]) - 1)

        if (r < len(board) - 1):
            print('right')
            is_edge = is_edge or self.bfs_is_edge(board, potential_starting_points, seen, (r+1, c))
        if (r > 0):
            print('left')
            is_edge = is_edge or self.bfs_is_edge(board, potential_starting_points, seen, (r-1, c))
        if (c < len(board[0]) - 1):
            print('down')
            is_edge = is_edge or self.bfs_is_edge(board, potential_starting_points, seen, (r, c+1))
        if (c > 0):
            print('up')
            is_edge = is_edge or self.bfs_is_edge(board, potential_starting_points, seen, (r, c-1))

        return is_edge

    def solve(self, board: List[List[str]]) -> None:
        """
        Do not return anything, modify board in-place instead.
        """
        potential_starting_points = set()
        for row in range(len(board)):
            for column in range(len(board[0])):
                if board[row][column] == 'O':
                    potential_starting_points.add((row, column))

        while len(potential_starting_points) > 0:
            start = next(iter(potential_starting_points))
            is_edge = self.bfs_is_edge(board, potential_starting_points, set(), start)
            print(start)
            print(is_edge)
            if not is_edge:
                self.bfs_capture(board, set(), start)

31070