Valid Triangle Number
Post · Apr 16, 2026
Sort the side lengths, fix the largest one at a time, and let the gap between two pointers count every valid pair against it in one step instead of testing them one by one.
3Sum
Post · Apr 10, 2026
Sort the array, fix one value as a moving target, and reuse the exact two-pointer proof from Two Sum II to sweep the rest, with a couple of extra duplicate-skipping rules layered on top.
Two Sum II
Post · Apr 5, 2026
A sorted array, two pointers closing in from both ends, and a proof that whichever side is off-target can be ruled out entirely rather than retried against a smaller search space.
Container With Most Water
Post · Mar 30, 2026
A row of walls, two pointers starting at the widest container, and a proof that moving the taller wall can never beat what you already have, so only the shorter side is ever worth moving.