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CoursesArray Patterns

Two Pointers

Lessons
9
Exercises
56
Minutes
57
  1. 1

    When Two Pointers Apply

    Spot the problems where two converging pointers beat checking every pair.

    Multiple choiceTap
    5 exercises
    4 min
  2. 2

    Two Sum II

    Use the sorted order to decide which pointer moves — and never rescan.

    Complete codeDebugMultiple choiceTrace
    6 exercises
    6 min
  3. 3

    Container With Most Water

    The shorter wall limits the area — so it is always the one that moves.

    Complete codeMultiple choiceTrace
    6 exercises
    6 min
  4. 4

    Move Zeroes

    Compact non-zero values in-place with reader/writer pointers, preserving their order.

    Complete codeDebugMultiple choiceTapTrace
    6 exercises
    6 min
  5. 5

    3Sum

    Sort, fix one element, and reduce the rest to a two-pointer pair search — skipping duplicates as you scan.

    Code orderMultiple choiceTrace
    6 exercises
    7 min
  6. 6

    Sort Colors

    Partition 0s, 1s, and 2s in one pass with three pointers — and learn why mid stays put after swapping with high.

    Complete codeDebugMultiple choiceTrace
    6 exercises
    6 min
  7. 7

    Two Pointers CheckpointCheckpoint

    No new concepts — transfer the island's converging-pointer rules to a fresh problem: counting valid triangles from sorted side lengths.

    DebugCode orderFill blankMultiple choiceTrace
    6 exercises
    6 min
  8. 8

    Two Pointers ReviewReview

    Mixed recap of the island: choosing a pointer setup, the move rule, reader/writer compaction, three-way partitioning, and dedup.

    Complete codeDebugMultiple choiceTapTrace
    7 exercises
    6 min
  9. 9

    Boss: Trapping Rain WaterBoss

    The classic hard problem, tamed: water at each bar is min(maxLeft, maxRight) - height, and two pointers settle whichever side's bound is already decided.

    Complete codeDebugCode orderMultiple choiceTrace
    8 exercises
    10 min
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Array Patterns is part of AlgoFox Pro

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