<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 __init__(self):
        self.regions = []
        self.visited = set()
        self.onBorder = False

    def getRegions(self, board, row, col, region):
        ROWS, COLS = len(board), len(board[0])
        if row < 0 or row >= ROWS or col < 0 or col >= COLS or (row, col) in self.visited or board[row][col] == "X":
            return
        
        ## If any of the region is on the border, then they can't be surrounded
        if row == 0 or row == ROWS - 1 or col == 0 or col == COLS - 1:
            self.onBorder = True

        self.visited.add((row, col))
        region.append((row, col))
        
        self.getRegions(board, row - 1, col, region)
        self.getRegions(board, row + 1, col, region)
        self.getRegions(board, row, col - 1, region)
        self.getRegions(board, row, col + 1, region)
        return [region, self.onBorder]

    def surroundRegions(self):
        pass

    def solve(self, board: List[List[str]]) -> None:
        """
        Do not return anything, modify board in-place instead.
        """
        ROWS, COLS = len(board), len(board[0])
        
        number_of_regions = 0
        for row in range(ROWS):
            for col in range(COLS):
                if (row, col) not in self.visited and board[row][col] == "O":
                    number_of_regions += 1
                    region = self.getRegions(board, row, col, [])
                    self.regions.append(region)
                    # Reset the onBorder flag to False when checking for next region
                    self.onBorder = False
        # print(number_of_regions)
        # print(self.regions)

        for region in self.regions:
            # Unpack the region into coordinates and onBorder flag
            coord, onBorder = region
            # If the region is not on the border
            # Iterate over all coordinates in this region
            # Mark these coordinates as "X" on the board to indicate that
            # they are surrounded
            if not onBorder:
                for r, c in coord:
                    board[r][c] = "X"
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