🗓️ 🗓️ All 90 Days Reference — DSA Roadmap

Every day has a specific deliverable: study the pattern, solve the listed problems, internalize the recognition trigger. Mark Done only when you can solve cold (no notes) in under 20 minutes.

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Phase 1 — Foundations (Days 1–15)

Day	Pattern	Problems to Solve
1	Prefix Sum basics	Running Sum of 1D Array, Find Pivot Index
2	Prefix Sum + HashMap	Subarray Sum Equals K, Range Sum Query
3	Prefix Product	Product of Array Except Self
4	Two Pointers basics	Two Sum II, Valid Palindrome
5	Two Pointers advanced	3Sum, Container With Most Water
6	Two Pointers hard	Trapping Rain Water, Sort Colors
7	Sliding Window fixed	Best Time to Buy/Sell Stock, Max Average Subarray
8	Sliding Window variable	Longest Substring No Repeat, Permutation in String
9	Sliding Window hard	Minimum Window Substring, Longest Repeating Char Replace
10	Binary Search basics	Binary Search, Search a 2D Matrix
11	Binary Search on rotated	Find Min in Rotated Array, Search in Rotated Array
12	Binary Search on answer	Koko Eating Bananas, Capacity to Ship Packages
13	Sort + Greedy	Merge Intervals, Non-Overlapping Intervals
14	Sort + Heap	Meeting Rooms II
15	Phase 1 Review	Sliding Window Maximum, Split Array Largest Sum (timed mock)

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Phase 2 — Core Data Structures (Days 16–35)

Day	Pattern	Problems to Solve
16	Linked List basics	Reverse Linked List, Merge Two Sorted Lists
17	Fast/Slow Pointer	Linked List Cycle, Linked List Cycle II
18	Linked List manipulation	Remove Nth From End, Reorder List
19	Linked List hard	Merge K Sorted Lists, Copy List with Random Pointer
20	Stack basics	Valid Parentheses, Min Stack
21	Monotonic Stack	Daily Temperatures, Evaluate RPN
22	Monotonic Stack hard	Largest Rectangle in Histogram
23	HashMap basics	Two Sum, Valid Anagram
24	HashMap intermediate	Group Anagrams, Top K Frequent Elements
25	HashMap hard	Longest Consecutive Sequence, Design HashMap
26	Tree DFS basics	Maximum Depth, Invert Binary Tree, Same Tree
27	Tree DFS validation	Validate BST, Diameter of Binary Tree
28	Tree DFS LCA	Lowest Common Ancestor of BST
29	Tree BFS	Binary Tree Level Order Traversal, Right Side View
30	Tree construction	Construct Tree from Preorder/Inorder
31	Tree hard	Binary Tree Maximum Path Sum, Kth Smallest in BST
32	Tree serialization	Serialize/Deserialize Binary Tree
33	Monotonic Deque	Sliding Window Maximum
34	Queue design	Design Circular Queue, Number of Recent Calls
35	Phase 2 Review	8-problem timed mock (mixed patterns)

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Phase 3 — Advanced Data Structures (Days 36–55)

Day	Pattern	Problems to Solve
36	Heap basics	Kth Largest Element, Last Stone Weight
37	Heap Top-K	K Closest Points to Origin, Top K Frequent
38	Heap + Greedy	Task Scheduler
39	Two Heaps	Find Median from Data Stream
40	Heap hard	Merge K Sorted Lists
41	Graph DFS	Number of Islands, Clone Graph
42	Graph DFS grid	Pacific Atlantic Water Flow, Surrounded Regions
43	Topological Sort	Course Schedule, Course Schedule II
44	Graph BFS	Word Ladder, Rotting Oranges
45	Graph review	Graph Valid Tree
46	Dijkstra	Network Delay Time
47	Dijkstra + state	Cheapest Flights Within K Stops
48	Dijkstra/Binary Search	Path with Minimum Effort
49	Bellman-Ford concept	Path with Maximum Probability
50	Union-Find basics	Number of Connected Components
51	Union-Find intermediate	Redundant Connection, Number of Provinces
52	Union-Find hard	Accounts Merge
53	Trie basics	Implement Trie, Design Add and Search Words
54	Trie hard	Word Search II
55	Phase 3 Review	5-problem timed mock (Heap/Graph/UnionFind/Trie)

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Phase 4 — Core Algorithms (Days 56–75)

Day	Pattern	Problems to Solve
56	Backtracking basics	Subsets, Permutations
57	Backtracking combo	Combination Sum, Generate Parentheses
58	Backtracking constraint	N-Queens
59	Backtracking grid	Word Search
60	Backtracking partition	Palindrome Partitioning
61	DP 1D basics	Climbing Stairs, House Robber
62	DP 1D intermediate	House Robber II, Coin Change
63	DP 1D LIS	Longest Increasing Subsequence (both O(n^2) and O(n log n))
64	DP 1D strings	Word Break, Decode Ways, Max Product Subarray
65	DP Grid	Unique Paths, Minimum Path Sum
66	DP 0/1 Knapsack	Partition Equal Subset Sum
67	DP Two Strings	Longest Common Subsequence
68	DP Two Strings hard	Edit Distance, Coin Change II
69	Greedy basics	Jump Game, Jump Game II
70	Greedy intermediate	Gas Station, Partition Labels
71	Greedy intervals	Non-overlapping Intervals
72	Divide and Conquer	Merge Sort (Sort an Array)
73	Divide and Conquer Quick Select	Kth Largest Element via Quick Select
74	D&C / Classic	Maximum Subarray, Majority Element
75	Phase 4 Review	6-problem timed mock (Backtrack/DP/Greedy mixed)

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Phase 5 — Advanced & Interview Prep (Days 76–90)

Day	Pattern	Problems to Solve
76	Bitmask DP basics	Partition to K Equal Sum Subsets
77	Bitmask DP + BFS	Shortest Path Visiting All Nodes
78	Bitmask DP hard	Find the Shortest Superstring
79	Interval DP	Burst Balloons
80	Interval DP hard	Minimum Cost to Merge Stones
81	State Machine DP	Best Time to Buy/Sell with Cooldown + Fee
82	MST Prim's	Min Cost to Connect All Points
83	MST Kruskal's	Connecting Cities with Minimum Cost
84	Dijkstra advanced	Swim in Rising Water
85	Design problems	LRU Cache, LFU Cache
86	Mock Interview 1	2 medium problems, Arrays/Strings/Two Pointer, full 35-min process
87	Mock Interview 2	2 medium problems, Trees/Graphs, full 35-min process
88	Mock Interview 3	2 medium-hard DP problems, full 35-min process
89	Mock Interview 4	1 easy + 1 hard, full 45-min interview simulation
90	Final Review	Re-solve 10 problems cold across all patterns. Write your own pattern cheat sheet.

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Daily ritual

1. Open this table. Find today's row.
2. Read the pattern explanation in the phase page before coding.
3. Solve each listed problem WITHOUT looking at the solution first (give it 20-25 min).
4. If stuck: look at the pattern hint only, not the full solution. Try again.
5. After solving (or after seeing the solution): re-type the solution from scratch without copying.
6. Log in tracker: Problems solved, Solved without hints, Time taken, Key insight.
7. Any problem you couldn't solve cold goes in Problems to revisit — redo it in 3 days.