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🧠 Weekly Challenge
Algorithm Challenge: DFS + Grid-Based Perimeter Logic
Find the largest perimeter of an island in a given 2D grid, where 1 represents land and 0 represents water. An island is a group of adjacent land cells. A "land cell" is any cell in the grid that contains the value 1, representing land. These cells can be connected horizontally or vertically to form an island. The perimeter of an island is the number of water cells surrounding it (including grid edges). Your function should return the maximum perimeter of any island found in the grid.
This technical problem is used by Meta, Airbnb, and Google to assess your understanding of grid traversal, DFS, and edge-aware perimeter calculations.
Approach Hints:
Struggling to get started? Here are technical breadcrumbs from the optimal solution:
Use Depth-First Search (DFS) to explore each island.
Track visited cells with a separate visited grid.
For each unvisited land cell (1), collect all connected land cells using DFS.
Define a helper function neighbors(r, c) to return valid 4-directional neighbours.
For each land cell, count:
-> +1 to perimeter for every adjacent water cell
-> +1 for every time the cell touches the edge of the grid
Track the max perimeter as you process each island.
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