Problems › Techniques
The roadmap
Every problem here trains a named topic — a hash map, a sliding window, a binary search. Some are concepts, the material itself; the rest are patterns, the moves you make with it, which is the part an interview is really testing. The five stages below run in teaching order: each leans on the one above it, so working down the page takes you from writing a loop to the patterns interviews ask about.
1 Foundations
Arithmetic you can trust, and the two containers everything else is built on.
2 Counting and shaping
Turn a pile of records into an answer: tally it, order it, read it.
3 Scanning a sequence
One pass instead of two loops — the move that turns O(n²) into O(n).
4 Structures and search
Pick the shape that fits the problem and the search gets easy.
- Stacksconcept · 9 problems
- Binary searchpattern · 9 problems
- Intervalsconcept · 16 problems
- Gridsconcept · 9 problems
5 Ways of thinking
Less about a data structure than about the argument you make for an answer.