<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>

from collections import deque

class Solution:
    def solve(self, board: List[List[str]]) -> None:
        """
        Do not return anything, modify board in-place instead.
        """
        if not len(board) or not len(board[0]):
            return
        
        ROW, COL = len(board), len(board[0])
        OFFSET = [(0,1), (0,-1), (1,0), (-1,0)]
        visited: Set[Tuple[int, int]] = set()

        def get_neighbors(r: int, c: int) -> List[Tuple[int, int]]:
            neighbors: List[Tuple[int, int]] = []
            
            for dr, dc in OFFSET:
                nr, nc = r + dr, c + dc
                
                if (nr, nc) in visited:
                    continue

                if (0 <= nr < ROW) and (0 <= nc < COL) and board[nr][nc] == "O":
                    visited.add((nr, nc))
                    neighbors.append((nr, nc))

            return neighbors


        def traverse(r: int, c: int) -> List[Tuple[int, int]]:
            queue: deque[Tuple[int, int]] = deque([(r, c)])
            traversed: List[Tuple[int, int]] = []

            while queue:
                r, c = queue.popleft()
                visited.add((r, c))
                traversed.append((r, c))

                for nr, nc in get_neighbors(r, c):
                    visited.add((nr, nc))
                    queue.append((nr, nc))

            return traversed

        def process_region(region: List[Tuple[int, int]]) -> None:
            # should not process if any of the region is on the border
            should_not_process = any([
                r == 0
                or r == ROW - 1 
                or c == 0
                or c == COL - 1 
                for r, c in region]
            )
            
            if should_not_process:
                return

            for r, c in region:
                board[r][c] = "X"

        for r in range(ROW):
            for c in range(COL):
                if board[r][c] == "O" and (r, c) not in visited:
                    region: List[Tuple[int, int]] = traverse(r, c)
                    process_region(region)
24770