LeetCode 695 Max Area of Island - Core Idea

Here is the step-by-step approach:

$1.$ Loop through every cell in the grid.

$2.$ If you find a land cell ($1$) that has not been visited, trigger DFS from that cell.

$3.$ DFS marks the cell as visited (set to $0$), then recursively calls DFS on all $4$ neighbors. Each recursive call returns the area of that branch.

$4.$ DFS returns $1$ (current cell) plus the sum of areas from all neighbors.

$5.$ Track the maximum area returned by any DFS call.

$6.$ Return the maximum after visiting all cells.

The recursion builds the area bottom-up, starting from leaf cells and accumulating as it returns.