Use a graph traversal algorithm like DFS or BFS to explore each unvisited land cell and mark all connected land cells as visited, incrementing the island count for each traversal. Alternatively, use Union-Find to group adjacent land cells and count distinct sets.
Pro tip: Discuss the trade-offs between DFS (recursive, may cause stack overflow for large grids) and BFS (iterative, uses queue) and mention that Union-Find is efficient for dynamic connectivity but may be overkill for static grids.
Confirm the definition of adjacency (4-directional), input format (2D array of integers), and expected output (integer count). Ask about edge cases like empty grid or all water.
Select a traversal method (DFS or BFS) or Union-Find. Explain why it's suitable: DFS/BFS are simple and efficient for this problem; Union-Find can be used but may be less intuitive.
Describe the steps: iterate through each cell; if it's land and unvisited, increment island count and perform traversal to mark all connected land cells as visited.
State time complexity O(M*N) where M and N are grid dimensions, as each cell is visited once. Space complexity O(M*N) in worst case for recursion stack or queue.
Mention handling empty grid, using visited matrix or modifying grid in-place to save space, and potential stack overflow with DFS for large grids.
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