What does the The Ladder puzzle teach?
Find the longest run of strictly increasing values that keeps the original order. Greedily taking every bigger number can trap you in a short chain — the LIS sometimes skips an early value to climb higher later.
Why do interviews ask about this?
Longest increasing subsequence is the canonical greedy-fails-DP-wins problem — taking every larger value dead-ends; the fix is the LIS dynamic program (or the O(n log n) patience-sorting variant).
How is it scored?
The engine computes the provably-optimal answer for the exact instance you played (dynamic programming, shortest-path, or exhaustive search — never a heuristic) and scores your attempt as a percentage of it. No login needed to see your score.