<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 solve(self, board: List[List[str]]) -> None:
        """
        Do not return anything, modify board in-place instead.
        """
        DELTAS = [(0, -1), (1, 0), (0, 1), (-1, 0)]

        m = len(board)
        n = len(board[0])

        def is_valid(i, j):
            return (i > -1) and (i < m) and (j > -1) and (j < n)

        def expand(i, j):
            neighbors = []
            is_edge = False
            for (dx, dy) in DELTAS:
                nx, ny = i + dx, j + dy
                if is_valid(nx, ny):
                    if board[nx][ny] == 'O':
                        neighbors.append((nx, ny))
                else:
                    is_edge = True
            return neighbors, is_edge

        def scan(i, j):
            print("S", i, j)
            island = set()
            is_edge = False
            q = [(i,j)]
            while len(q) > 0:
                curr_index = q.pop(0)
                if curr_index not in island:
                    island.add(curr_index)
                    neighbors, is_curr_edge = expand(curr_index[0], curr_index[1])
                    is_edge = is_edge or is_curr_edge
                    q.extend(neighbors)
            print(island)
            print(is_edge)
            return island, is_edge

        seen_edge_islands = set()
        for i in range(m):
            for j in range(n):
                if board[i][j] == 'O' and (i, j) not in seen_edge_islands:
                    island, is_edge = scan(i, j)
                    if is_edge:
                        seen_edge_islands = seen_edge_islands.union(island)
                    else:
                        for (x,y) in island:
                            board[x][y] = 'X'

            
        
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