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CoursesTrees & Graphs

Grid Traversal

Lessons
9
Exercises
56
Minutes
61
  1. 1

    Grids Are Graphs

    A grid is a graph in disguise: spread cell to cell with DFS or BFS, mark visited, and always bounds-check first.

    Code orderMultiple choiceTap
    6 exercises
    5 min
  2. 2

    Flood Fill

    Recolor the start's connected component of same-colored pixels — and dodge the same-color infinite loop.

    Complete codeDebugMultiple choiceTrace
    6 exercises
    6 min
  3. 3

    Number of Islands

    Count DFS launches, not land cells: each launch sinks one whole island.

    Complete codeDebugMultiple choiceTapTrace
    6 exercises
    7 min
  4. 4

    Max Area of Island

    Flood fill that reports back: each DFS call returns 1 + its four neighbors' areas, and the caller keeps the max.

    Complete codeDebugMultiple choiceTrace
    6 exercises
    6 min
  5. 5

    Surrounded Regions

    Don't hunt the surrounded regions — flood from the border 'O's, mark the survivors safe, and flip everything else.

    Complete codeDebugCode orderMultiple choiceTrace
    6 exercises
    7 min
  6. 6

    01 Matrix

    Multi-source BFS: drop every 0 into the queue at distance 0 and let one wave label the whole grid.

    Complete codeDebugMultiple choiceTrace
    6 exercises
    7 min
  7. 7

    Grid Traversal CheckpointCheckpoint

    No new concepts — transfer the island's grid moves to unseen problems: counting exposed edges, islands that dodge the border, BFS through a maze, and painting everything the border can reach.

    Complete codeCode orderMultiple choiceTrace
    6 exercises
    7 min
  8. 8

    Grid Traversal ReviewReview

    Mixed recap of the island: DFS-sink vs multi-source BFS, the border-inversion trick, in-place marking vs a visited array, bounds-check-first discipline, and why it all costs O(mn).

    Complete codeDebugCode orderMultiple choice
    6 exercises
    6 min
  9. 9

    Boss: Rotting OrangesBoss

    The island's final test: every rotten orange spreads at once, so minutes are BFS LAYERS from ALL sources — not steps of one walker. Seed the whole queue at minute 0, count the fresh, and answer -1 only when a fresh orange is unreachable.

    Complete codeDebugCode orderMultiple choiceTrace
    8 exercises
    10 min
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Trees & Graphs is part of AlgoFox Pro

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