U USACO Prep

USACO 2018 February — the whole contest, all four divisions.

Every USACO round is 4 divisions × 3 problems = 12 problems total. This page indexes the February 2018 round end-to-end: Bronze through Platinum, with the official statement link, the key idea, complexity target, and a runnable C++ reference for each problem on the per-division pages.

Bronze (all 3) → Silver (all 3) → Gold (all 3) → Platinum (all 3) →
Authoritative source. All problem titles, constraints, and results below are taken from the official February 2018 results page on usaco.org: usaco.org/index.php?page=feb18results. Each problem links to its official statement (statements live at usaco.org/index.php?page=viewproblem2&cpid=…, cpids 807–818).

Round metadata

ContestUSACO 2018 February
WindowRoughly Feb 23–26, 2018 (4-day window, single 4-hour personal timer)
Length per division4 hours (Dec/Jan/Feb format; US Open is the 5-hour round)
Problems per division3
Total problems12 (Bronze 1–3, Silver 1–3, Gold 1–3, Platinum 1–3)
ScoringIOI-style partial credit, 1000 points per problem, 3000 max per division
Allowed languagesC, C++11, C++17, Java, Python 2.7, Python 3.6 (C++17 is the default for serious climbers)
Promotion cutoffsSet per-contest by USACO; check the results page for exact thresholds.

The contest at a glance

Bronze

Bronze · 3 problems

1. Teleportation — minimum tractor distance to move manure when a single teleporter (x↔y) is available; case analysis on |a−b| vs. |a−x|+|y−b|.

2. Hoofball — N cows on a line pass to the nearest neighbor; count how many distinct cows must start with a ball so every cow receives one (graph in-degree analysis).

3. Taming the Herd — given a log of consecutive days since last "breakout," count the minimum and maximum possible number of breakouts consistent with unknowns.

Open Bronze write-up →
 Silver

Silver · 3 problems

1. Rest Stops — Bessie and Farmer John walk a path at different speeds; choose rest stops to maximize total tastiness collected (greedy from the right).

2. Snow Boots — stack of B boot pairs (depth, step) must traverse N snowy tiles; minimum boots to discard (DP / simulation, N,B ≤ 250).

3. Teleportation — N manure piles each have a source and destination; with one teleporter at (x, y) for free use, minimize total hauling distance over all x (sweep on critical points).

Open Silver write-up →
 Gold

Gold · 3 problems

1. Snow Boots — N tiles with depths, B boots with (depth tolerance, max step); which boots can complete the path? (offline sweep + sorted set of dangerous tiles).

2. Directory Traversal — pick the directory in a filesystem tree that minimizes the sum of relative path lengths to all files (tree rerooting DP).

3. Taming the Herd — Gold version: count assignments of unknowns producing exactly K breakouts (DP on prefixes, O(N³)).

Open Gold write-up →
 Platinum

Platinum · 3 problems

1. Slingshot — N slingshots (x→y in time t) and M manure piles; minimum delivery time per pile using at most one slingshot (offline + 4 segment trees on transformed coordinates).

2. New Barns — online incremental forest; after each "build", answer distance from a queried node to the farthest node in its component (LCA + diameter endpoints update).

3. Cow Gymnasts — count "magical" stack configurations on N circular platforms where falling preserves stack heights; number-theoretic divisor sum (N ≤ 1012).

Open Platinum write-up →

How to use this set

  1. Pick your division. Open the full division page and read the three statements before writing any code.
  2. Solve P1 first, P2 if time, P3 only if you're cruising. February problem 1s are usually the cheapest points.
  3. Time-box. 4 hours total. Don't spend more than ~90 minutes on a single problem without a working subtask submission.
  4. Compare to the reference C++. Each problem on the division page has a ~30–50 line reference solution. If yours is much longer, ask why.
  5. Verify with the editorial. Official editorials are linked from each problem page on usaco.org.