<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:
    bool dfs(vector<vector<int>>& grid, int row, int col){
        //grid[row][col] = 2;
        int n = grid.size(), m = grid[0].size();
        if(row == n - 1 || col == m - 1 || row == 0 || col == 0){
            grid[row][col] = -1;
            return false;
        }
        grid[row][col] = 1;
        vector<bool> dir(4, false);

        if(grid[row + 1][col] >= 1){
            dir[0] = true;
        } else if(grid[row + 1][col] == 0){
            dir[0] = dfs(grid, row + 1, col);
        } else{
            dir[0] = false;
        }

        if(grid[row][col + 1] >= 1){
            dir[1] = true;
        } else if(grid[row][col + 1] == 0){
            dir[1] = dfs(grid, row, col + 1);
        } else{
            dir[1] = false;
        }

        if(grid[row - 1][col] >= 1){
            dir[2] = true;
        } else if(grid[row - 1][col] == 0){
            dir[2] = dfs(grid, row - 1, col);
        } else{
            dir[2] = false;
        }

        if(grid[row][col - 1] >= 1){
            dir[3] = true;
        } else if(grid[row][col - 1] == 0){
            dir[3] = dfs(grid, row, col - 1);
        } else{
            dir[3] = false;
        }

        if(dir[0] && dir[1] && dir[2] && dir[3]){
            grid[row][col] = 2;
            return true;
        } else{
            grid[row][col] = -1;
            return false;
        }
    }

    int closedIsland(vector<vector<int>>& grid) {
        int result = 0;
        for(int i = 0; i < grid.size(); i++){
            for(int j = 0; j < grid[0].size(); j++){
                if(grid[i][j] == 0){
                    if(dfs(grid, i, j)){
                        result++;
                    }
                }
            }
        }
        return result;
    }
};
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