Problem Statement

Given an m x n binary matrix grid, where 0 represents a sea cell and 1 represents a land cell, return the number of land cells in grid from which you can't reach to the boundary in any number of moves.

In a single move, you can walk from one cell to any cell, which is 4-directionally adjacent to the current cell.

Examples

Example 1:

• Input: grid =

[[0, 0, 0, 1],
 [1, 0, 1, 0],
 [0, 1, 1, 0],
 [0, 0, 0, 0]]

• Output: 3
• Justification: The three land cells in the center, which are at (1, 2), (2, 1), and (2, 2) positions, are surrounded by sea cells and cannot reach the boundary.

Examples

Example 1:

• Input: grid =

[[0, 0, 0, 1],
[1, 0, 1, 0],
[0, 1, 1, 0],
[0, 0, 0, 0]]

• Output: 3
• Justification: The three land cells in the center are surrounded by sea cells and cannot reach the boundary.

Example 2:

• Input: grid =

[[0, 1, 0],
[1, 1, 1],
[0, 1, 0]]

• Output: 0
• Justification: All land cells can connect to the edge either directly or through other land cells.

Example 3:

• Input: grid =

[[0, 0, 0, 0, 0],
[0, 1, 1, 1, 0],
[0, 1, 0, 1, 0],
[0, 1, 1, 1, 0],
[0, 0, 0, 0, 0]]

• Output: 8
• Justification: The eight land cells in the middle are surrounded by sea cells and cannot reach the boundary.

Constraints:

• m == grid.length
• n == grid[i].length
• 1 <= m, n <= 500
• grid[i][j] is either 0 or 1.

Try it yourself

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