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Java-based LeetCode algorithm problem solutions, regularly updated

There is a newer version: 1.24

1254\. Number of Closed Islands

Medium

Given a 2D `grid` consists of `0s` (land) and `1s` (water). An _island_ is a maximal 4-directionally connected group of `0s` and a _closed island_ is an island **totally** (all left, top, right, bottom) surrounded by `1s.`

Return the number of _closed islands_.

**Example 1:**

![](https://assets.leetcode.com/uploads/2019/10/31/sample_3_1610.png)

**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).

**Example 2:**

![](https://assets.leetcode.com/uploads/2019/10/31/sample_4_1610.png)

**Input:** grid = [[0,0,1,0,0],[0,1,0,1,0],[0,1,1,1,0]]

**Output:** 1

**Example 3:**

**Input:** grid = [[1,1,1,1,1,1,1], 
                   [1,0,0,0,0,0,1], 
                   [1,0,1,1,1,0,1], 
                   [1,0,1,0,1,0,1], 
                   [1,0,1,1,1,0,1], 
                   [1,0,0,0,0,0,1], 
                   [1,1,1,1,1,1,1]]

**Output:** 2

**Constraints:**

*   `1 <= grid.length, grid[0].length <= 100`
*   `0 <= grid[i][j] <=1`