Arrays & Strings

Beginner

Every codebase is built on sequences. These patterns — two pointers, sliding windows, prefix sums — show up in log processing, data pipelines, and performance-critical loops, not just interviews.

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8/12

Foundations

Two SumHash Map Lookup

Best Time to Buy and Sell StockKadane's Variant

Contains DuplicateSet Usage

Valid AnagramFrequency Count

Core

Product of Array Except SelfPrefix/Suffix

Maximum SubarrayKadane's Algorithm

Container With Most WaterTwo Pointers

3SumTwo Pointers + Sort

Intermediate

Longest Substring Without RepeatingSliding Window

10

Minimum Window SubstringSliding Window

Hard25m

11

Group AnagramsHash Map Grouping

Medium15m

12

Trapping Rain WaterTwo Pointers

Hard25m