Number of Islands
Count connected components on a grid with flood fill from every unvisited land cell.
Decision · step 3 of 18Flood Fill: Count the islands
Island 1. Pop (0, 0). 2 neighbours still land: (1, 0), (0, 1). Paint and queue them.
What you will see
Each island is flooded with its own number.
Cost
| Best | O(r * c) |
|---|---|
| Average | O(r * c) |
| Worst | O(r * c) |
| Space | O(r * c) |
How you work with it here
play it through, step one change at a time, scrub to any step, run it on your own input, predict what happens next, try operations in any order.
Screen readers: Vertices announce name, neighbours and state (in queue, visited, current); each step announces which vertex is processed and which neighbours are discovered.
Reduced motion: Frontier and visited changes are crossfades; the traversal edge is emphasized without a travelling token.