<p>Given a 2D&nbsp;<code>grid</code> consists of <code>0s</code> (land)&nbsp;and <code>1s</code> (water).&nbsp; An <em>island</em> is a maximal 4-directionally connected group of <code><font face="monospace">0</font>s</code> and a <em>closed island</em>&nbsp;is an island <strong>totally</strong>&nbsp;(all left, top, right, bottom) surrounded by <code>1s.</code></p>

<p>Return the number of <em>closed islands</em>.</p>

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

<p><img alt="" src="https://assets.leetcode.com/uploads/2019/10/31/sample_3_1610.png" style="width: 240px; height: 120px;" /></p>

<pre>
<strong>Input:</strong> grid = [[1,1,1,1,1,1,1,0],[1,0,0,0,0,1,1,0],[1,0,1,0,1,1,1,0],[1,0,0,0,0,1,0,1],[1,1,1,1,1,1,1,0]]
<strong>Output:</strong> 2
<strong>Explanation:</strong> 
Islands in gray are closed because they are completely surrounded by water (group of 1s).</pre>

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

<p><img alt="" src="https://assets.leetcode.com/uploads/2019/10/31/sample_4_1610.png" style="width: 160px; height: 80px;" /></p>

<pre>
<strong>Input:</strong> grid = [[0,0,1,0,0],[0,1,0,1,0],[0,1,1,1,0]]
<strong>Output:</strong> 1
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> grid = [[1,1,1,1,1,1,1],
&nbsp;              [1,0,0,0,0,0,1],
&nbsp;              [1,0,1,1,1,0,1],
&nbsp;              [1,0,1,0,1,0,1],
&nbsp;              [1,0,1,1,1,0,1],
&nbsp;              [1,0,0,0,0,0,1],
               [1,1,1,1,1,1,1]]
<strong>Output:</strong> 2
</pre>

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

<ul>
	<li><code>1 &lt;= grid.length, grid[0].length &lt;= 100</code></li>
	<li><code>0 &lt;= grid[i][j] &lt;=1</code></li>
</ul>

class Solution {
  public:
    int closedIsland(vector<vector<int>>&grid) {
      const int row = grid.size();
      const int col = grid[0].size();
      int res = 0;
      for (int i = 0; i < row; ++i) {
        for (int j = 0; j < col; ++j) {
          if (grid[i][j] == 0 && checkClosed(grid, i, j, row, col)) {
            ++res;
          }
        }
      }
      return res;
    }

  private:
    static constexpr bool IsEdge(const int i, const int j, const int row, const int col) {
      return i == 0 || i == row - 1 || j == 0 || j == col - 1;
    }
    static constexpr bool IsValidNode(const int i, const int j, const int row, const int col) {
      return i >= 0 && i < row && j >= 0 && j < col;
    }
    bool checkClosed(std::vector<std::vector<int>>&grid, int i, int j, const int row, const int col) {
      static thread_local std::queue<std::pair<int, int>> visitingNode;
      bool isClosed = true;
      visitingNode.push({i, j});
      while (!visitingNode.empty()) {
        auto [curRow, curCol] = visitingNode.front();
        visitingNode.pop();
        grid[curRow][curCol] = 1;

        if (IsEdge(curRow, curCol, row, col)) {
          isClosed = false;
        }
        for (const auto&[rowChange, colChange] : dirs_) {
          const int nextRow = curRow + rowChange;
          const int nextCol = curCol + colChange;
          if (!IsValidNode(nextRow, nextCol, row, col)) {
            continue;
          }

          if (grid[nextRow][nextCol] == 1) {
            continue;
          }

          visitingNode.push({nextRow, nextCol});
        }
      }
      return isClosed;
    }
    static constexpr std::array<std::pair<int, int>, 4> dirs_{{{1, 0}, {0, 1}, {-1, 0}, {0, -1}}};
};

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