Boundary

2 articles

dsa10 min read

Number of Enclaves — Boundary Flood Fill That Trips Up Candidates

LC 1020 Number of Enclaves asks you to count land cells that cannot reach the grid boundary. The trick is to flip the problem: flood-fill from the boundary inward, eliminating all reachable land, then count what remains.

March 19, 2026Read →

dsa9 min read

Number of Closed Islands — Boundary DFS + Interior Count

Count land islands fully surrounded by water (no border touch). Flood-fill border land first to eliminate open islands, then count remaining closed components.

March 19, 2026Read →