You are given an m $\times$ n binary matrix grid, where $0$ represents a sea cell and $1$ represents a land cell.

A move consists of walking from one land cell to another horizontally or vertically adjacent land cell, or walking off the boundary of the grid.

Return the number of land cells in grid from which it is impossible to walk off the boundary of the grid in any number of moves.

Constraints:

• m == grid.length

• n == grid[i].length

• $1 \leq$ m, n $\leq 500$

• grid[i][j] is either $0$ or $1$.

Now, let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Implement your solution in the following coding playground.