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Walls and Gates — Multi-Source BFS from Gates
Fill each empty room with distance to nearest gate. Multi-source BFS from all gates (0) simultaneously, walls (-1) are barriers.
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1276 articles
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Number of Enclaves — Boundary DFS Count
Count land cells that cannot reach the border. Boundary DFS marks all reachable land from borders, then count remaining land cells.
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Count Sub Islands — DFS Subset Check
Count islands in grid2 that are subsets of islands in grid1. DFS the island in grid2 and verify every cell is also land in grid1.
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Making a Large Island — DFS Color Map + Merge
Find the largest island after flipping exactly one 0 to 1. Color each island with DFS, store sizes, then check each 0 cell's unique neighbour islands.
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Pacific Atlantic Water Flow — Two-Source DFS
Find cells that can flow to both Pacific and Atlantic oceans. Run DFS backwards from each ocean border, find intersection.
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