<p>An <code>n x n</code> grid is composed of <code>1 x 1</code> squares where each <code>1 x 1</code> square consists of a <code>&#39;/&#39;</code>, <code>&#39;\&#39;</code>, or blank space <code>&#39; &#39;</code>. These characters divide the square into contiguous regions.</p>

<p>Given the grid <code>grid</code> represented as a string array, return <em>the number of regions</em>.</p>

<p>Note that backslash characters are escaped, so a <code>&#39;\&#39;</code> is represented as <code>&#39;\\&#39;</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2018/12/15/1.png" style="width: 200px; height: 200px;" />
<pre>
<strong>Input:</strong> grid = [&quot; /&quot;,&quot;/ &quot;]
<strong>Output:</strong> 2
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2018/12/15/2.png" style="width: 200px; height: 198px;" />
<pre>
<strong>Input:</strong> grid = [&quot; /&quot;,&quot;  &quot;]
<strong>Output:</strong> 1
</pre>

<p><strong class="example">Example 3:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2018/12/15/4.png" style="width: 200px; height: 200px;" />
<pre>
<strong>Input:</strong> grid = [&quot;/\\&quot;,&quot;\\/&quot;]
<strong>Output:</strong> 5
<strong>Explanation: </strong>Recall that because \ characters are escaped, &quot;\\/&quot; refers to \/, and &quot;/\\&quot; refers to /\.
</pre>

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

<ul>
	<li><code>n == grid.length == grid[i].length</code></li>
	<li><code>1 &lt;= n &lt;= 30</code></li>
	<li><code>grid[i][j]</code> is either <code>&#39;/&#39;</code>, <code>&#39;\&#39;</code>, or <code>&#39; &#39;</code>.</li>
</ul>

class Solution {
public:
    int regionsBySlashes(vector<string>& grid) {
        int n = grid.size();
        int m = 3 * n;
        vector<vector<int>> matrix(m, vector<int>(m));
        for(int i = 0; i < n; ++i) {
            for(int j = 0; j < n; ++j) {
                if (grid[i][j] == ' ')
                    continue;
                if (grid[i][j] == '/') {
                    for (int k = 0; k < 3; ++k) {
                        int x = i*3+k;
                        int y = j*3+2-k;
                        matrix[x][y] = 1;
                    }
                }
                if (grid[i][j] == '\\') {
                    for (int k = 0; k < 3; ++k) {
                        int x = i*3+k;
                        int y = j*3+k;
                        matrix[x][y] = 1;
                    }
                }
            }
        }


        vector<int> dirs = {0,-1,0,1,0};
        int ans = 0;
        for (int i = 0; i < m; ++i) {
            for (int j = 0; j < m; ++j) {
                if (matrix[i][j] == 1)
                    continue;
                ++ans;
                stack<pair<int,int>> s;
                s.push({i,j});
                while(!s.empty()) {
                    auto [r,c] = s.top();
                    s.pop();
                    matrix[r][c] = 1;
                    for (int d = 0; d < 4; ++d) {
                        int x = r + dirs[d];
                        int y = c + dirs[d+1];
                        if (x >= 0 && x < m && y >= 0 && y < m && matrix[x][y] == 0) {
                            s.push({x,y});
                        }
                    }
                }
            }
        }
        return ans;
    }
};
18953