Topic 68: LeetCode / NeetCode 150 — Pattern Recognition & Intuition

The single biggest jump in coding-interview competence is moving from "let me try to solve this problem" to "this is a sliding-window problem; here's the template." This folder trains that move.

🔥 Read these first:

  • LEETCODE_PATTERNS_DEEP_DIVE.md — The 30-second triage; all 18 NeetCode 150 pattern categories (Arrays & Hashing, Two Pointers, Sliding Window, Stack, Binary Search, Linked List, Trees, Tries, Heap, Backtracking, Graphs, Advanced Graphs, 1D DP, 2D DP, Greedy, Intervals, Math/Geometry, Bit Manipulation), each with: recognition signals, mental model, code templates, 5-10 representative problems with quick walkthroughs, common variants, and traps. Plus problem-to-pattern transformation tricks, complexity reasoning cheatsheet, common interview traps, the 5-step problem-solving protocol, and a 9-week drilling routine.
  • INTERVIEW_GRILL.md — 165 pattern-recognition active-recall questions across A–O. Read a problem statement, name the pattern in <30 seconds. 8-week drill plan mapped to NeetCode 150.

Worked-solutions files (simplest-optimal Python, intuitive explanations, memory hooks, pressure-tested templates — 135 problems total):

  • SOLUTIONS_ARRAYS_HASHING_SLIDING_WINDOW.md — 9 Arrays & Hashing + 6 Sliding Window problems.
  • SOLUTIONS_TWO_POINTERS_STACK.md — 5 Two Pointers + 7 Stack problems.
  • SOLUTIONS_BINARY_SEARCH_LINKED_LIST.md — 7 Binary Search + 11 Linked List problems.
  • SOLUTIONS_TREES.md — 15 Tree problems.
  • SOLUTIONS_HEAP_BACKTRACKING.md — 7 Heap/Priority Queue + 10 Backtracking problems.
  • SOLUTIONS_GRAPHS_ADVANCED.md — 13 Graph + 6 Advanced Graph problems.
  • SOLUTIONS_DP.md — 12 1-D DP + 11 2-D DP problems.
  • SOLUTIONS_GREEDY_MATH_GEOMETRY.md — 8 Greedy + 8 Math & Geometry problems.

Why this folder

NeetCode 150 / Blind 75 / Grind 75 are problem lists. Solving them one-by-one without organizing them by pattern is grinding. The 18 categories in NeetCode are signal: they tell you the underlying templates the lists are testing. If you can recognize "this is sliding window" in 30 seconds, you've already done the hardest part of the interview.

What this folder gives you

  • The 30-second triage. Input shape → output shape → constraints → structural cues → pattern.
  • Per-pattern playbook. Recognition signals, mental model, copy-pasteable templates in Python, representative problems, traps.
  • Transformation tricks. "Sort first," "build a graph," "binary-search on the answer," "treat 2D as 1D" — the moves that turn hard problems into known patterns.
  • Complexity cheatsheet. Map to acceptable algorithm classes.
  • The 5-step protocol to deploy in any coding interview: Understand → Examples → Brute force → Optimize → Code.
  • 9-week drilling plan with daily routine.
  • 165-question grill focused on pattern recognition.

Core insight

For any problem, do the 30-second triage by input shape, output shape, constraints, and structural cues; then match to one of 18 patterns; then deploy the template.

Cross-references

  • 50_ml_coding_interview_patterns/ — ML coding (numpy / from scratch ML algorithms), complementary.
  • 58_whiteboard_derivations/ — math derivations (different rounds).
  • 67_frontier_intuitive_questions/ — probabilistic reasoning questions (different round type).

How to use

  1. Read LEETCODE_PATTERNS_DEEP_DIVE.md once cover to cover. Note weak patterns.
  2. For each weak pattern, drill 5+ problems on NeetCode / LeetCode.
  3. Drill INTERVIEW_GRILL.md weekly until you hit 130+/165.
  4. Re-read §1 (triage), §20 (transformations), §22 (traps), §23 (protocol) every Sunday.
  5. Mock interviews in the last 2 weeks; mixed problems on shuffle.

Suggested external resources

  • NeetCode 150 — neetcode.io/practice — the curated list this folder is organized around.
  • NeetCode YouTube — the gold standard for pattern walkthroughs.
  • Blind 75 — LeetCode discuss; smaller curated list.
  • Grind 75 — same author as Blind 75, slightly extended.
  • CSES Problem Set — for competitive-programming depth.

The single sentence to remember: read fast, triage fast, name the pattern out loud, deploy the template, then code.