Back
Level 1·FOUNDATION

Foundation: Cost, Recursion & the One-Pass Move

Measure what code costs, run a call stack by hand, then learn the scans that beat checking every pair.

PROGRESS
0/6
lessons done
0%
Learning objectives
  • Big O by counting, not by memorising
  • Recursion: the base case and the stack
  • Hash maps: one pass instead of every pair
  • Two pointers and the sliding window
  • Binary search, written correctly
What to expect
  • Animated interactive explainers per concept
  • Real code examples with production gotchas
  • Step-by-step breakdowns you can follow along
  • Interview tips embedded in every lesson
~8h · 6 lessons
Lessons, 0 of 6 complete
  • 01
    Big-OINTERACTIVE

    Count the steps by hand as n doubles, then name the shape

    ~80 min
  • RecursionINTERACTIVE

    Run the call stack with your finger; the base case turns it around

    ~80 min
  • Hash MapsINTERACTIVE

    One pass, writing down what you have seen

    ~80 min
  • Two PointersINTERACTIVE

    Two fingers closing in; prove why skipping is safe

    ~80 min
  • Sliding WindowINTERACTIVE

    Grow and shrink, never restart

    ~80 min
  • Binary SearchINTERACTIVE

    Halve it, and prove the half you threw away was innocent

    ~80 min
Data Structures & Algorithms · Level 1 · TheSimplifiedTech