Grokking Graph Algorithms for Coding Interviews
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Number of Closed Islands (easy)
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Problem Statement

You are given a 2D matrix containing only 1s (land) and 0s (water).

An island is a connected set of 1s (land) and is surrounded by either an edge or 0s (water). Each cell is considered connected to other cells horizontally or vertically (not diagonally).

A closed island is an island that is totally surrounded by 0s (i.e., water). This means all horizontally and vertically connected cells of a closed island are water. This also means that, by definition, a closed island can't touch an edge (as then the edge cells are not connected to any water cell).

Write a function to find the number of closed islands in the given matrix.

Example 1

Input: matrix =

Image

Output: 1 Explanation: The given matrix has two islands, but only the highlighted island is a closed island. The other island is touching the boundary that's why is is not considered a closed island.

Example 2

Input: matrix =

Image

Output: 2

Explanation: The given matrix has two islands and both of them are closed islands.

Constraints:

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

Try it yourself

Try solving this question here:

Python3
Python3
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