LeetCode 354 Russian Doll Envelopes - Walkthrough

Envelopes are $(w, h)$ pairs. You can nest envelope $a$ inside $b$ if $a.w < b.w$ and $a.h < b.h$. Sort by width ascending, then by height descending within same width. This keeps we can't nest envelopes with same width.

Now run LIS on the heights. The descending tie-break prevents using two envelopes with same width. Example: $[(5,4), (6,4), (6,7), (2,3)]$ → sorted: $[(2,3), (5,4), (6,7), (6,4)]$ → heights: $[3, 4, 7, 4]$ → LIS: $3$.