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Study roadmap

37 patterns ordered densest-first. Foundations and core interview tiers ship complete; advanced/expert entries may still be stubs. For every problem write: which pattern, what changed from the template, what would break it, and whether you recognized it in 90 seconds.

Phases

  1. Phase 0 · Foundations: Foundations (1 to 7): window, pointers, binary search, hashing, prefix sums. Highest interview density.
  2. Phase 1: Core interview, essential + recommended after foundations (orders ~8-32): stacks, heaps, intervals, graphs, trees, tries, greedy, DP, bits, and more.
  3. Phase 2: Hard modes, advanced + expert (orders ~19-37): union-find, topo, segment trees, MST, KMP, bitmask DP, meet-in-the-middle, reservoir sampling.

Showing 1 to 8 of 37

  1. Phase 0 · Foundations · Pattern 1

    Sliding Window

    Longest, shortest, or valid contiguous ranges over arrays and strings.

    EssentialStart here
    -/6
    LC 3 · mediumLC 76 · hardLC 209 · mediumLC 424 · mediumLC 567 · mediumLC 904 · medium

  2. Phase 0 · Foundations · Pattern 2

    Two Pointers

    Sorted arrays, pair conditions, or coordinated movement from both ends.

    EssentialStart here
    -/6
    LC 11 · mediumLC 15 · mediumLC 16 · mediumLC 18 · mediumLC 42 · hardLC 167 · medium

  3. Phase 0 · Foundations · Pattern 3

    Fast & Slow Pointers

    Linked-list cycles, middle nodes, and fixed pointer gaps.

    EssentialStart here
    -/6
    LC 19 · mediumLC 141 · easyLC 142 · mediumLC 160 · easyLC 234 · easyLC 876 · easy

  4. Phase 0 · Foundations · Pattern 4

    Binary Search

    Halve a sorted or monotonic search space until you pin the answer.

    EssentialStart here
    -/6
    LC 33 · mediumLC 34 · mediumLC 35 · easyLC 153 · mediumLC 162 · mediumLC 704 · easy

  5. Phase 0 · Foundations · Pattern 5

    Binary Search on Answer

    Binary search the answer value itself; check if a candidate is feasible in linear time.

    EssentialStart here
    -/6
    LC 410 · hardLC 774 · hardLC 875 · mediumLC 1011 · mediumLC 1283 · mediumLC 1482 · medium

  6. Phase 0 · Foundations · Pattern 6

    Hashing

    O(1) average lookup, frequency counting, grouping, and complement checks.

    EssentialStart here
    -/6
    LC 1 · easyLC 49 · mediumLC 128 · mediumLC 217 · easyLC 242 · easyLC 347 · medium

  7. Phase 0 · Foundations · Pattern 7

    Prefix Sum

    Precompute running sums so any range sum is O(1); pair with maps for subarray sum counts.

    EssentialStart here
    -/6
    LC 303 · easyLC 523 · mediumLC 560 · mediumLC 724 · easyLC 930 · mediumLC 974 · medium

  8. Phase 1 · Pattern 8

    Difference Array

    Range updates in O(1); rebuild the array with a prefix pass.

    RecommendedContinue
    -/6
    LC 370 · mediumLC 1094 · mediumLC 1109 · mediumLC 1893 · easyLC 1943 · mediumLC 2381 · medium