Chains
Problem families that escalate. Each chain takes one idea and removes a little more of what made it easy.
- Intersection of Two ChainsTwo paths that merge share a tail. Find the first shared node with a set, or with two pointers that swap starts.3 problemsSep 22 2026
- Rebuilding a NumberTwo lines of arithmetic - peel the last digit off, append a digit on - and a choice of base. Every problem here is those two lines wearing different clothes.15 problemsSep 22 2026
- Lowest Common AncestorOne question - where do the paths to two nodes split - answered with steadily less information about the tree.9 problemsSep 20 2026
- Two SumThe hash map is the right answer exactly once. Every later question in this family takes away the thing that made it right.15 problemsSep 20 2026