Appendix J: 90-Day Study Plan

A comprehensive week-by-week plan to master all DSA topics. This plan assumes 3-4 hours of study per day.

Overview

• Duration: 13 weeks (90 days)
• Daily commitment: 3-4 hours
• Weekly pattern: 5 days learning + 1 day practice + 1 day review
• Total problems: ~300-400
• Goal: Complete mastery of all major DSA topics

Week 1: Arrays & Strings (Days 1-7)

Day 1: Array Fundamentals

• Array basics: memory layout, time complexity
• Two-pointer technique
• Problems: Two Sum, Remove Duplicates from Sorted Array
• Practice: 2-3 easy problems

Day 2: String Fundamentals

• String operations, ASCII/Unicode
• String comparison, substring extraction
• Problems: Valid Anagram, Reverse String
• Practice: 2-3 easy problems

Day 3: Sliding Window

• Fixed-size and variable-size windows
• Problems: Maximum Subarray (Kadane’s), Longest Substring Without Repeating Characters
• Practice: 2-3 medium problems

Day 4: Two Pointers

• Two pointers on sorted arrays
• Problems: 3Sum, Container With Most Water
• Practice: 2-3 medium problems

Day 5: Prefix Sums & Hashing

• Prefix sum technique
• Hash map for frequency counting
• Problems: Product of Array Except Self, Subarray Sum Equals K
• Practice: 2-3 medium problems

Day 6: Practice Day

• Solve 5-6 problems on arrays and strings
• Focus on medium difficulty
• Review any topics you struggled with

Day 7: Review Day

• Review all concepts from the week
• Redo any problems you couldn’t solve
• Update your notes and cheat sheets

Week 2: Linked Lists & Stacks/Queues (Days 8-14)

Day 8: Singly Linked List

• Node structure, traversal, insertion, deletion
• Problems: Reverse Linked List, Merge Two Sorted Lists
• Practice: 2-3 easy problems

Day 9: Linked List Techniques

• Fast/slow pointers (Floyd’s algorithm)
• Problems: Detect Cycle, Find Cycle Start, Middle of Linked List
• Practice: 2-3 medium problems

Day 10: Advanced Linked List

• LRU Cache implementation
• Problems: Merge K Sorted Lists, Remove Nth Node From End
• Practice: 2-3 medium problems

Day 11: Stack Fundamentals

• Stack operations, applications
• Problems: Valid Parentheses, Min Stack
• Practice: 2-3 easy/medium problems

Day 12: Monotonic Stack

• Monotonic stack technique
• Problems: Daily Temperatures, Next Greater Element, Largest Rectangle in Histogram
• Practice: 2-3 medium problems

Day 13: Queue & Deque

• Queue operations, deque
• Problems: Sliding Window Maximum, Implement Queue using Stacks
• Practice: 2-3 medium problems

Day 14: Review Day

• Review linked lists, stacks, queues
• Redo challenging problems
• Update notes

Week 3: Trees - Basics (Days 15-21)

Day 15: Binary Tree Basics

• Tree terminology, traversals (pre/in/post/level order)
• Problems: Maximum Depth, Same Tree, Invert Tree
• Practice: 2-3 easy problems

Day 16: Tree Traversals

• Iterative traversals
• Morris traversal (optional)
• Problems: Binary Tree Inorder Traversal, Level Order Traversal
• Practice: 2-3 medium problems

Day 17: Tree Properties

• Balanced tree, symmetric tree, path sum
• Problems: Balanced Binary Tree, Symmetric Tree, Path Sum
• Practice: 2-3 easy/medium problems

Day 18: BST Operations

• BST search, insert, delete
• Problems: Validate BST, Kth Smallest Element in BST
• Practice: 2-3 medium problems

Day 19: Tree Construction

• Build tree from traversals
• Problems: Construct Binary Tree from Preorder and Inorder
• Practice: 2-3 medium problems

Day 20: LCA & Path Problems

• Lowest Common Ancestor
• Problems: LCA of Binary Tree, Binary Tree Maximum Path Sum
• Practice: 2-3 medium/hard problems

Day 21: Review Day

• Review all tree concepts
• Redo challenging problems
• Update notes

Week 4: Trees - Advanced (Days 22-28)

Day 22: Tree Serialization

• Serialize/deserialize trees
• Problems: Serialize and Deserialize Binary Tree
• Practice: 2-3 medium problems

Day 23: Trie

• Trie structure, insert, search, prefix
• Problems: Implement Trie, Word Search II
• Practice: 2-3 medium problems

Day 24: Segment Tree

• Range queries and updates
• Problems: Range Sum Query, Range Minimum Query
• Practice: 2-3 medium problems

Day 25: Fenwick Tree

• Binary Indexed Tree
• Problems: Range Sum Query - Mutable
• Practice: 2-3 medium problems

Day 26: BST Advanced

• BST iterators, recovery
• Problems: BST Iterator, Recover BST
• Practice: 2-3 medium/hard problems

Day 27: N-ary Trees

• N-ary tree traversals
• Problems: N-ary Tree Level Order Traversal
• Practice: 2-3 medium problems

Day 28: Review Day

• Review advanced tree topics
• Redo challenging problems
• Update notes

Week 5: Graphs - Basics (Days 29-35)

Day 29: Graph Representation

• Adjacency list, adjacency matrix
• BFS, DFS implementations
• Problems: Number of Islands, Clone Graph
• Practice: 2-3 medium problems

Day 30: BFS Applications

• Shortest path in unweighted graph
• Problems: Rotting Oranges, Word Ladder
• Practice: 2-3 medium problems

Day 31: DFS Applications

• Connected components, cycle detection
• Problems: Number of Connected Components, Graph Valid Tree
• Practice: 2-3 medium problems

Day 32: Topological Sort

• DFS-based and BFS-based (Kahn’s)
• Problems: Course Schedule, Alien Dictionary
• Practice: 2-3 medium problems

Day 33: Union-Find

• DSU with path compression and union by rank
• Problems: Redundant Connection, Number of Provinces
• Practice: 2-3 medium problems

Day 34: Grid Problems

• Grid BFS/DFS
• Problems: Pacific Atlantic Water Flow, Surrounded Regions
• Practice: 2-3 medium problems

Day 35: Review Day

• Review graph basics
• Redo challenging problems
• Update notes

Week 6: Graphs - Advanced (Days 36-42)

Day 36: Dijkstra’s Algorithm

• Shortest path with non-negative weights
• Problems: Network Delay Time, Cheapest Flights Within K Stops
• Practice: 2-3 medium problems

Day 37: Bellman-Ford

• Shortest path with negative edges
• Problems: Negative Weight Cycle Detection
• Practice: 2-3 medium problems

Day 38: Floyd-Warshall

• All-pairs shortest path
• Problems: Find the City With the Smallest Number of Neighbors
• Practice: 2-3 medium problems

Day 39: Minimum Spanning Tree

• Kruskal’s and Prim’s algorithms
• Problems: Min Cost to Connect All Points
• Practice: 2-3 medium problems

Day 40: Strongly Connected Components

• Tarjan’s and Kosaraju’s algorithms
• Problems: Critical Connections in a Network
• Practice: 2-3 medium/hard problems

Day 41: Max Flow (Optional)

• Ford-Fulkerson, Edmonds-Karp
• Problems: Maximum Bipartite Matching
• Practice: 1-2 hard problems

Day 42: Review Day

• Review advanced graph topics
• Redo challenging problems
• Update notes

Week 7: Dynamic Programming - 1D (Days 43-49)

Day 43: DP Fundamentals

• Overlapping subproblems, optimal substructure
• Memoization vs tabulation
• Problems: Fibonacci, Climbing Stairs
• Practice: 2-3 easy problems

Day 44: 1D DP

• House Robber, Maximum Subarray
• Problems: House Robber, Maximum Product Subarray
• Practice: 2-3 medium problems

Day 45: DP on Strings

• LCS, Edit Distance
• Problems: Longest Common Subsequence, Edit Distance
• Practice: 2-3 medium problems

Day 46: LIS & Variants

• Longest Increasing Subsequence
• Problems: LIS, Russian Doll Envelopes
• Practice: 2-3 medium problems

Day 47: Knapsack Problems

• 0/1 Knapsack, Unbounded Knapsack
• Problems: Partition Equal Subset Sum, Coin Change
• Practice: 2-3 medium problems

Day 48: Decode Ways & Jump Game

• DP with conditions
• Problems: Decode Ways, Jump Game, Jump Game II
• Practice: 2-3 medium problems

Day 49: Review Day

• Review 1D DP
• Redo challenging problems
• Update notes

Week 8: Dynamic Programming - 2D & Advanced (Days 50-56)

Day 50: Grid DP

• Unique Paths, Minimum Path Sum
• Problems: Unique Paths, Minimum Path Sum, Dungeon Game
• Practice: 2-3 medium problems

Day 51: Interval DP

• Matrix Chain Multiplication
• Problems: Burst Balloons, Palindrome Partitioning
• Practice: 2-3 hard problems

Day 52: Bitmask DP

• TSP, Assignment Problem
• Problems: Shortest Path Visiting All Nodes
• Practice: 2-3 hard problems

Day 53: Digit DP

• Count numbers with property
• Problems: Count Numbers With Unique Digits
• Practice: 2-3 medium problems

Day 54: Tree DP

• DP on trees
• Problems: Binary Tree Maximum Path Sum, House Robber III
• Practice: 2-3 medium problems

Day 55: Stock Problems

• Buy/sell stock with various constraints
• Problems: Best Time to Buy and Sell Stock (all variants)
• Practice: 2-3 medium/hard problems

Day 56: Review Day

• Review advanced DP
• Redo challenging problems
• Update notes

Week 9: Binary Search & Sorting (Days 57-63)

Day 57: Binary Search Basics

• Standard binary search, variants
• Problems: Binary Search, Search Insert Position
• Practice: 2-3 easy problems

Day 58: Binary Search on Answer

• Binary search on the answer space
• Problems: Capacity to Ship Packages, Koko Eating Bananas
• Practice: 2-3 medium problems

Day 59: Binary Search in Rotated Arrays

• Search in rotated sorted array
• Problems: Find Minimum in Rotated Sorted Array, Search in Rotated Array
• Practice: 2-3 medium problems

Day 60: Sorting Algorithms

• Merge sort, quicksort, heapsort
• Problems: Sort an Array, Kth Largest Element
• Practice: 2-3 medium problems

Day 61: Quickselect

• Partition-based selection
• Problems: Kth Largest Element, Top K Frequent Elements
• Practice: 2-3 medium problems

Day 62: Custom Sorting

• Custom comparators, merge intervals
• Problems: Merge Intervals, Largest Number
• Practice: 2-3 medium problems

Day 63: Review Day

• Review binary search and sorting
• Redo challenging problems
• Update notes

Week 10: Heaps, Greedy, & Backtracking (Days 64-70)

Day 64: Heap Fundamentals

• Min-heap, max-heap, priority queue
• Problems: Kth Largest Element, Last Stone Weight
• Practice: 2-3 easy/medium problems

Day 65: Heap Applications

• Find median, merge k sorted
• Problems: Find Median from Data Stream, Merge K Sorted Lists
• Practice: 2-3 medium/hard problems

Day 66: Greedy Basics

• Greedy choice property
• Problems: Jump Game, Jump Game II
• Practice: 2-3 medium problems

Day 67: Greedy Intervals

• Interval scheduling
• Problems: Non-overlapping Intervals, Meeting Rooms II
• Practice: 2-3 medium problems

Day 68: Backtracking Basics

• Subsets, permutations, combinations
• Problems: Subsets, Permutations, Combination Sum
• Practice: 2-3 medium problems

Day 69: Backtracking Advanced

• N-Queens, Sudoku Solver
• Problems: N-Queens, Word Search
• Practice: 2-3 medium/hard problems

Day 70: Review Day

• Review heaps, greedy, backtracking
• Redo challenging problems
• Update notes

Week 11: Math & Bit Manipulation (Days 71-77)

Day 71: Number Theory

• GCD, LCM, primes, sieve
• Problems: Count Primes, GCD/LCM
• Practice: 2-3 medium problems

Day 72: Modular Arithmetic

• Modular inverse, fast power
• Problems: Super Pow, Modular operations
• Practice: 2-3 medium problems

Day 73: Combinatorics

• Factorials, combinations, permutations
• Problems: Pascal’s Triangle, Unique Paths (math solution)
• Practice: 2-3 medium problems

Day 74: Bit Manipulation Basics

• AND, OR, XOR, shifts
• Problems: Single Number, Power of Two
• Practice: 2-3 easy problems

Day 75: Bit Manipulation Advanced

• Subset enumeration, bitmask tricks
• Problems: Subsets (bitmask), Counting Bits
• Practice: 2-3 medium problems

Day 76: Matrix & Geometry

• Matrix operations, rotation
• Problems: Rotate Image, Spiral Matrix
• Practice: 2-3 medium problems

Day 77: Review Day

• Review math and bit manipulation
• Redo challenging problems
• Update notes

Week 12: Advanced Topics (Days 78-84)

Day 78: String Matching

• KMP, Z Algorithm
• Problems: Implement strStr(), Repeated Substring Pattern
• Practice: 2-3 medium problems

Day 79: Sliding Window Advanced

• Sliding window with hash map
• Problems: Minimum Window Substring, Substring with Concatenation
• Practice: 2-3 hard problems

Day 80: Monotonic Stack/Queue Advanced

• Complex applications
• Problems: Trapping Rain Water, Maximal Rectangle
• Practice: 2-3 hard problems

Day 81: Design Problems

• LRU Cache, LFU Cache
• Problems: LRU Cache, Design Twitter
• Practice: 2-3 medium/hard problems

Day 82: System Design Basics (Optional)

• Scalability concepts
• Load balancing, caching, database sharding
• Read: Introduction to system design

Day 83: Mock Interview Practice

• Do 2-3 mock interviews
• Focus on communication and problem-solving process
• Review feedback

Day 84: Review Day

• Review advanced topics
• Redo challenging problems
• Update notes

Week 13: Final Review & Mock Interviews (Days 85-90)

Day 85: Weak Areas Review

• Identify your weakest 3-4 topics
• Review concepts and redo problems
• Focus on understanding, not memorization

Day 86: Pattern Recognition

• Review all problem patterns
• Practice identifying which technique to use
• Solve 5-6 mixed problems

Day 87: Mock Interview 1

• Full mock interview (45-60 minutes)
• Focus on communication and time management
• Review feedback

Day 88: Mock Interview 2

• Full mock interview (45-60 minutes)
• Focus on edge cases and testing
• Review feedback

Day 89: Final Review

• Review cheat sheets and notes
• Redo 3-4 problems you found most challenging
• Prepare questions for interviews

Day 90: Rest & Prepare

• Light review only
• Get good sleep
• Prepare your environment for interviews
• Review the Interview Checklist (Appendix F)

Daily Schedule Template

Weekly Goals

Progress Tracking

Use this table to track your progress:

Consistency is key. Even on days when you don’t feel like studying, do at least 30 minutes. Small daily progress compounds into mastery over 90 days.