Problems/1020. Number of Enclaves

1020. Number of Enclaves

MediumMatrixGraphDFSBFS

You are given a 2D matrix of size m x n containing land cells (1s) and water cells (0s).

A land cell is an enclave if it is impossible to walk off the edge of the grid by stepping only 4-directionally on land cells. Find the total count of such enclaved land cells in the grid.

Example 1

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

Output: 3

There are three land cells in the center that are enclaves because they are surrounded by water and cannot reach any edge.

Example 2

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

Output: 0

All land cells are connected to the top edge, meaning they can all reach the boundary. Thus, there are 0 enclaves.

Example 3

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

Output: 1

The single land cell in the center has no path to the boundary, forming 1 enclave.

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