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Shortest Path in Binary Matrix — BFS 8-Directional
Find shortest clear path from top-left to bottom-right in binary matrix using 8-directional BFS. Return path length or -1.
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As Far from Land as Possible — Multi-Source BFS
Find the water cell farthest from any land. Multi-source BFS from all land cells gives each water cell its min distance to land.
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Word Search — DFS with Backtracking
Search for a word in a grid by moving to adjacent cells without reuse. DFS with backtracking: mark visited, recurse, unmark.
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Number of Distinct Islands — DFS Shape Hashing
Count islands with distinct shapes. Encode each island's DFS traversal path as a string to capture shape, store in a set.
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Number of Closed Islands — Boundary DFS + Count
Count islands fully surrounded by water (no border touch). Flood-fill border land first, then count remaining connected land components.
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