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>

closedIsland

Number of Closed Islands

Depth-First Search

Breadth-First Search

Union Find

Array

Matrix

二维矩阵 <code>grid</code>&nbsp;由 <code>0</code>&nbsp;（土地）和 <code>1</code>&nbsp;（水）组成。岛是由最大的4个方向连通的 <code>0</code>&nbsp;组成的群，封闭岛是一个&nbsp;<code>完全</code> 由1包围（左、上、右、下）的岛。

请返回 封闭岛屿 的数目。

&nbsp;

示例 1：

<img alt="" src="https://assets.leetcode.com/uploads/2019/10/31/sample_3_1610.png" style="height: 151px; width: 240px;" />

<pre>
输入：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]]
输出：2
解释：
灰色区域的岛屿是封闭岛屿，因为这座岛屿完全被水域包围（即被 1 区域包围）。</pre>

示例 2：

<img src="https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2019/11/07/sample_4_1610.png" style="height: 98px; width: 160px;" />

<pre>
输入：grid = [[0,0,1,0,0],[0,1,0,1,0],[0,1,1,1,0]]
输出：1
</pre>

示例 3：

<pre>
输入：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]]
输出：2
</pre>

&nbsp;

提示：

<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>