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Senior Java DSA Master - Study Guide

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A structured, FAANG-level Data Structures & Algorithms study guide for Senior Java Developers.

Philosophy

Knowing why you chose a Deque over a Stack or how HashMap resizing affects your O(n) time is what separates a Senior from a Junior candidate.

This guide follows the “Enhanced Senior Java DSA Master” format:

  • Brute Force vs. Optimal code side-by-side (Java only)
  • Java Architecture Insights explaining why specific data structures are chosen
  • ASCII visualizations for pointer/state tracing
  • Curated problem lists split into “Bread & Butter” and “FAANG Aha!” tiers

Start Here

File What it is
TEMPLATES.md All 21 algorithm templates on one page — the night-before-the-interview cheat sheet
MAANG-Prep/README.md 5-month interview plan: DSA lists, System Design, LLD, Java/Spring, Behavioural, Healthcare-AI
MAANG-Prep/STUDY-PLAN.md Week-by-week schedule mapped onto the pattern folders below
15-Blind-75/pattern-guide.md The curated 75-problem interview set

Every NN-Pattern/pattern-guide.md now opens with ## 0. The Template (Copy-Paste Skeleton) — the reusable Java skeleton for that pattern, plus the “knobs” you change per problem. Read §0 first, then the rest of the guide.

Pattern Roadmap (Study Sequence)

# Pattern Directory Focus Area
0 Foundations 00-Foundations/ Big O, Arrays, Java Tips, Trees
1 Two Pointers 01-Two-Pointers/ Sorted Arrays / Pairs
2 Sliding Window 02-Sliding-Window/ Subarrays / Substrings
3 Hashing / Frequency Maps 03-Hashing-Frequency-Maps/ O(1) Lookups / Counting
4 Fast & Slow Pointers 04-Fast-And-Slow-Pointers/ Linked List Cycles / Middle
5 Merge Intervals 05-Merge-Intervals/ Overlapping Ranges
6 Cyclic Sort 06-Cyclic-Sort/ Problems involving “1 to N”
7 Linked List Reversal 07-Linked-List-Reversal/ In-place Pointer Manipulation
8 BFS (Breadth-First Search) 08-BFS/ Tree Levels / Shortest Path
9 DFS (Depth-First Search) 09-DFS/ Tree Paths / Exhaustive Search
10 Two Heaps 10-Two-Heaps/ Median / Scheduling
11 Backtracking / Subsets 11-Backtracking-Subsets/ Combinations / Permutations
12 Binary Search (Modified) 12-Binary-Search/ Sorted Search Space
13 Top ‘K’ Elements 13-Top-K-Elements/ PriorityQueues / Heaps
14 Dynamic Programming 14-Dynamic-Programming/ Optimization / Subproblems
15 Blind 75 (by category) 15-Blind-75/ Curated 75-problem interview list
16 Graph Patterns 16-Graph-Patterns/ BFS/DFS/Topo/Union-Find/Dijkstra
17 Union-Find (DSU) 17-Union-Find/ Dynamic connectivity / grouping
18 Tries 18-Tries/ Prefix search / autocomplete
19 Greedy 19-Greedy/ Sort + sweep / interval selection
20 Monotonic Stack 20-Monotonic-Stack/ Next/previous greater or smaller
21 Stacks & Queues 21-Stacks-And-Queues/ LIFO / FIFO / monotonic deque / design
— MAANG Interview Prep MAANG-Prep/ DSA lists, System Design, LLD, Java/Spring, Behavioural

Directory Structure

DSA Study/
├── README.md                          (this file)
├── 00-Foundations/
│   ├── big-o-and-arrays.md
│   └── tree-fundamentals.md
├── 01-Two-Pointers/
│   ├── pattern-guide.md
│   └── problems/
├── 02-Sliding-Window/
│   ├── pattern-guide.md
│   └── problems/
├── ...                                (each pattern follows the same structure)
├── 14-Dynamic-Programming/
│   ├── pattern-guide.md
│   └── problems/
│       ├── 01-knapsack-0-1.md
│       ├── 02-house-robber.md
│       └── 03-house-robber-ii.md
├── 15-Blind-75/                       ← Curated 75-problem set, organized by category
│   ├── pattern-guide.md
│   ├── README.md
│   ├── interview-tips-and-strategies.md
│   ├── Array/                         (pattern-guide.md + 10 problems)
│   ├── Binary/                        (pattern-guide.md +  5 problems)
│   ├── Dynamic-Programming/           (pattern-guide.md + 11 problems)
│   ├── Graph/                         (pattern-guide.md +  8 problems)
│   ├── Heap/                          (pattern-guide.md +  3 problems)
│   ├── Interval/                      (pattern-guide.md +  4 problems)
│   ├── Linked-List/                   (pattern-guide.md +  6 problems)
│   ├── Matrix/                        (pattern-guide.md +  4 problems)
│   ├── String/                        (pattern-guide.md + 10 problems)
│   ├── Tree/                          (pattern-guide.md + 11 problems)
│   └── Trie/                          (pattern-guide.md +  3 problems)
├── 16-Graph-Patterns/                 ← BFS/DFS/Topo/Union-Find/Dijkstra/Bellman-Ford
│   ├── pattern-guide.md
│   └── problems/                      (LC 200, 207, 210, 547, 684, 743, 994, …)
├── 17-Union-Find/pattern-guide.md     ← DSU with path compression + union by rank
├── 18-Tries/pattern-guide.md          ← prefix trees, wildcard search, Word Search II
├── 19-Greedy/pattern-guide.md         ← sort-key selection, greedy-vs-DP discriminator
├── 20-Monotonic-Stack/                ← NEXT/PREVIOUS greater or smaller
│   ├── pattern-guide.md
│   └── problems/                      (LC 739, 496, 84)
├── 21-Stacks-And-Queues/              ← LIFO / FIFO / monotonic deque / design questions
│   ├── pattern-guide.md
│   └── problems/                      (LC 20, 232, 239, 994, 622)
├── MAANG-Prep/                        ← merged in from TestingArea/MAANG
│   ├── README.md                      (index + 5-month plan + daily cadence)
│   ├── STUDY-PLAN.md                  (20-week schedule)
│   ├── RESUME-VALIDATION.md           (scored resume review + bullet rewrites)
│   ├── 01-DSA/top-questions.md        (per-company pattern matrix, Must-Do 50)
│   ├── 02-System-Design/top-questions.md
│   ├── 03-LLD/top-questions.md
│   ├── 04-Java-Spring/top-questions.md
│   ├── 05-Behavioral/amazon-lp-stories.md
│   └── 06-Healthcare-AI/differentiator-notes.md
├── TEMPLATES.md                       ← ALL 21 templates on one page
└── Prompts/
    ├── pattern-master-prompt.md
    └── interview-problem-prompt.md

diagram 2

DSA Study/
├── README.md                              ← Master roadmap & study guide
├── 00-Foundations/
│   ├── big-o-and-arrays.md                ← Big O + Java Collections cheat sheet
│   └── tree-fundamentals.md               ← Tree roadmap + TreeNode class (from data2.md)
├── 01-Two-Pointers/pattern-guide.md       ← Full pattern breakdown
├── 02-Sliding-Window/pattern-guide.md
├── 03-Hashing-Frequency-Maps/pattern-guide.md
├── 04-Fast-And-Slow-Pointers/pattern-guide.md
├── 05-Merge-Intervals/pattern-guide.md
├── 06-Cyclic-Sort/pattern-guide.md
├── 07-Linked-List-Reversal/pattern-guide.md
├── 08-BFS/
│   ├── pattern-guide.md
│   └── problems/01-binary-tree-level-order-traversal.md  ← from pattern.md
├── 09-DFS/
│   ├── pattern-guide.md
│   └── problems/
│       ├── 01-maximum-depth-of-binary-tree.md             ← from data1.md
│       └── 02-lowest-common-ancestor.md                   ← from data3.md
├── 10-Two-Heaps/pattern-guide.md
├── 11-Backtracking-Subsets/pattern-guide.md
├── 12-Binary-Search/pattern-guide.md
├── 13-Top-K-Elements/pattern-guide.md
├── 14-Dynamic-Programming/
│   ├── pattern-guide.md                   ← 5 core DP patterns (from DP data.md)
│   └── problems/
│       ├── 01-knapsack-0-1.md             ← from DP data.md
│       ├── 02-house-robber.md             ← from DP data.md (converted to Java)
│       └── 03-house-robber-ii.md          ← from DP data.md (converted to Java)
└── Prompts/
    ├── pattern-master-prompt.md           ← Enhanced prompt template
    └── interview-problem-prompt.md        ← FAANG interview walkthrough prompt

Each pattern directory contains:

  • pattern-guide.md - Full pattern breakdown (identification, pseudocode, tricks, Java insights)
  • problems/ - Individual .md files per problem with brute force + optimal Java code

How to Use This Guide

  1. Study patterns in order - each builds on previous ones
  2. For each pattern, read pattern-guide.md — start with ## 0. The Template, memorise the skeleton, then read the rest for the mental model. TEMPLATES.md collects all 21 skeletons on one page for revision.
  3. Solve problems from the problems/ directory - start with “Bread & Butter”, then tackle “FAANG Aha!”
  4. Use the prompts in Prompts/ to generate deep-dives on any new pattern or problem
  5. All code is Java - production-grade, with architecture insights

Implementation Gap Strategy

Since you already understand theory but struggle with code:

  1. Draw it First - trace indices (i, j, left, right) on paper for small inputs
  2. Pseudocode Before Code - write comments in Java explaining logic before implementing
  3. Master Java Collections - Map.getOrDefault(), ArrayDeque for stacks/queues, PriorityQueue for heaps
  4. Time yourself - aim to solve Easy in 10 min, Medium in 20 min, Hard in 40 min

===================================================

All done. Here’s the complete summary of what was created:

Summary: 56 New Problem Solution Files Created

62 total problem files now exist across all 15 pattern directories (6 existed before, 56 are new). Every new file follows your enhanced prompt template with:

  1. Algorithm & Pseudocode - Clear, high-level logic breakdown
  2. Step-by-Step Beginner Analysis - The “Why” behind each line
  3. Dry Run - Sample input traced through every iteration with tables
  4. Java Solutions - Both Brute Force AND Optimal approaches (Java only)
  5. Java vs. Others Edge - Java-specific tricks, Collections, pitfalls vs C++/Python
  6. Complexity Summary - Time/Space comparison table

Files by Pattern Directory

Pattern New Problems Added
00-Foundations LC 1929, LC 121, LC 238, LC 41 (4 files)
01-Two-Pointers LC 125, LC 283, LC 344, LC 977 (4 files)
02-Sliding-Window LC 209, LC 643, LC 219, LC 1004 (4 files)
03-Hashing LC 242, LC 217, LC 383, LC 560 (4 files)
04-Fast-Slow-Pointers LC 876, LC 202, LC 234, LC 83 (4 files)
05-Merge-Intervals LC 57, LC 252, LC 253, LC 986 (4 files)
06-Cyclic-Sort LC 448, LC 136, LC 645 (3 files)
07-Linked-List-Reversal LC 21, LC 234, LC 83, LC 160 (4 files)
08-BFS LC 107, LC 199, LC 637, LC 111 (4 new + 1 existing)
09-DFS LC 226, LC 100, LC 112 (3 new + 2 existing)
10-Two-Heaps LC 703, LC 1046, LC 215 (3 files)
11-Backtracking LC 46, LC 77, LC 39, LC 22 (4 files)
12-Binary-Search LC 704, LC 35, LC 34, LC 74, LC 278 (5 files)
13-Top-K-Elements LC 703, LC 973, LC 692 (3 files)
14-Dynamic-Programming LC 70, LC 322, LC 62, LC 300 (4 new + 3 existing)

All files are named with LC-<number> prefix in kebab-case and placed in the problems/ subdirectory of each pattern folder.