USACO 2015 US Open · Platinum · did not exist
Heads up. The 2015 US Open ran only three divisions — Bronze, Silver, and Gold. The
Platinum division was introduced for the 2015–16 season starting with the December 2015 contest, so
there is no Platinum tier or problems for the 2015 US Open. The
official results page
confirms only three divisions: "Below are the detailed results for each of the gold, silver, and bronze
contests."
Why this page exists
The site's per-contest layout reserves a Platinum slot for every round. For older contests where Platinum didn't run, the slot is preserved with a redirect-style note so the URL pattern stays predictable.
Where to find the first real Platinum problem set
- USACO 2015 December · Platinum — the first Platinum round. Results: usaco.org/index.php?page=dec15results. Local write-up: 2015-dec-platinum.html.
- USACO 2016 US Open · Platinum — the next US Open with a Platinum division. Local write-up: 2016-open-platinum.html.
If you want a "Platinum-grade" problem from 2015 US Open Gold
Three reasonable candidates that hit Platinum-territory thinking:
- Trapped in the Haybales (Gold) — the O(N log N) editorial solution uses sparse-table doubling on a "next blocking bale" function. Implementing that variant is squarely Platinum-grade.
- Palindromic Paths (Gold) — push N up to ~2000 and the O(N³) two-walker DP needs constant-factor tricks (bitset, SIMD-friendly inner loop) and rolling memory. Good rep for Platinum-style optimization.
- Googol — already interactive with bignum; the natural Platinum extension is "minimize queries with proof of optimality," which is a competitive-math micro-exercise.
Sanity check the claim
- Open the 2015 US Open results. Three section headers — no "Platinum."
- Compare to December 2015 results. Four section headers — Platinum debuts.
- The USACO history page notes the 2015–16 season as the year the Platinum division was added.