number-of-closed-islands

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Algorithms

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

Return the number of closed islands.

&nbsp;
Example 1:

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

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

Example 2:

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

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

Example 3:

<pre>
Input: 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]]
Output: 2
</pre>

&nbsp;
Constraints:

<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>