dsa2 min read
Surrounded Regions — Boundary DFS
Capture all 'O' regions not connected to the border. Classic boundary DFS: mark safe cells from edges, then flip remaining O to X.
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Boundary
3 articles
dsa1 min read
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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dsa1 min read
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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