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Phase 1: Foundation

Phase 1: Foundation (Weeks 1-8)

Phase 1 Patterns
Discovery
Arrays & Hashing
0 / 12 problems
Discovery
Two Pointers
0 / 10 problems
Discovery
Sliding Window
0 / 10 problems
Discovery
Stack
0 / 10 problems
Discovery
Binary Search
0 / 12 problems
Discovery
Linked List
0 / 12 problems
Discovery
Trees - Basics
0 / 12 problems
Objective
Master O(1) lookup patterns and array traversal fundamentals.
Why This Pattern
When frequency, existence, or pairing matters, hash maps reduce O(n²) to O(n).
Problems
Easy
1. Two Sum
Complement lookup reduces O(n²) to O(n).
Monday
Practice
Easy
217. Contains Duplicate
Set existence is O(1).
Monday
Practice
Easy
242. Valid Anagram
Character frequency counting.
Tuesday
Practice
Medium
49. Group Anagrams
Sorted string is the canonical key.
Tuesday
Practice
Medium
347. Top K Frequent Elements
Count first, then select top K.
Tuesday
Practice
Medium
238. Product of Array Except Self
Prefix/suffix products without division.
Wednesday
Practice
Medium
36. Valid Sudoku
Hash sets for row/col/box constraints.
Wednesday
Practice
Medium
271. Encode and Decode Strings
Length-prefixed serialization.
Wednesday
Practice
Medium
128. Longest Consecutive Sequence
Hash set for O(n) sequence detection.
Thursday
Practice
Easy
349. Intersection of Two Arrays
Basic set intersection.
Thursday
Practice
Easy
350. Intersection of Two Arrays II
Frequency map intersection.
Thursday
Practice
Easy
283. Move Zeroes
Two-pointer in-place rearrangement.
Friday
Practice
Deliverables
  • 12 derivation logs completed
  • 1 LTS pattern document written
  • Can articulate: 'When I need O(1) existence/frequency lookup, I use a hash map because...'