1254. Number of Closed Islands

https://leetcode.com/problems/number-of-closed-islands

Description

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:

**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:

**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

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