Learn it in order, from Big-O up
22 short lessons, about 2.3 hours in total, each ending in the techniques it leads into. Read straight through, or drop into whatever the interview asked about.
Foundations
4 lessons · 26m01Big-O NotationHow to measure whether code is fast or slow, before you ever run it.7m02ArraysThe simplest data structure: a numbered row of boxes in memory.6m03StringsText is just an array of characters, with a few sharp edges.6m04Hash Maps & SetsThe O(1) lookup machine behind half of all interview solutions.7m
Linear Structures
3 lessons · 16mSorting & Searching
2 lessons · 13mTrees
4 lessons · 24m10Trees & Binary TreesHierarchies of nodes, and the four ways to walk them.7m11Binary Search TreesA tree with an ordering rule that makes search O(log n).6m12Heaps & Priority QueuesAlways know the smallest (or largest) element, in O(log n) per update.6m13TriesA tree of characters that makes prefix search instant.5m
Graphs
3 lessons · 19mCore Techniques
5 lessons · 34m17RecursionSolve a problem by solving smaller copies of it, with a base case to stop.7m18BacktrackingTry a choice, explore, undo it. Systematic search over all possibilities.6m19Two Pointers & Sliding WindowTurn nested O(n²) loops into a single O(n) pass.7m20Dynamic Programming BasicsCache the answers to overlapping subproblems instead of recomputing them.8m21Greedy AlgorithmsTake the best local choice at every step, when that provably works.6m