U USACO Prep

USACO 2019 February — the whole contest, all four divisions.

Every USACO round is 4 divisions × 3 problems = 12 problems total. This page indexes the February 2019 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 2019 results page on usaco.org: usaco.org/index.php?page=feb19results. Each problem links to its official statement (statements live at usaco.org/index.php?page=viewproblem2&cpid=…, cpids 915–926).

Round metadata

ContestUSACO 2019 February
WindowRoughly Feb 22–25, 2019 (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. Sleepy Cow Herding — three cows on a number line; only endpoint cows may move, into a non-endpoint slot. Find min/max moves to reach 3 consecutive positions.

2. The Great Revegetation — assign one of 4 grass types to N pastures so every cow's two favorites differ; output the lexicographically smallest assignment (greedy).

3. Measuring Traffic — N sensors along a highway with on/off ramps and main-segment ranges; compute tightest possible inflow/outflow ranges (two-pass interval intersection).

Open Bronze write-up →
 Silver

Silver · 3 problems

1. Sleepy Cow Herding — generalize Bronze P1 to N cows: min moves via sliding window over sorted positions, max via gap arithmetic.

2. Painting the Barn — N axis-aligned rectangles on a 200×200 grid; total area covered by exactly K coats (2D difference array).

3. The Great Revegetation — only 2 grass types now, with 'S' (same) and 'D' (different) constraints; count valid assignments = 2#components with a 2-coloring feasibility check.

Open Silver write-up →
 Gold

Gold · 3 problems

1. Cow Land — tree with node values, support point update and path XOR query (Euler tour + BIT on XOR).

2. Dishwashing — Bessie pushes plates onto monotone soapy stacks (a "patience sorting" structure); find longest prefix whose clean output is sorted.

3. Painting the Barn — Silver P2 plus: paint up to two extra disjoint rectangles to maximize area at exactly K coats (200×200 prefix sums + best-rectangle DP).

Open Gold write-up →
 Platinum

Platinum · 3 problems

1. Cow Dating — pick a contiguous interval of independent Bernoulli trials to maximize P(exactly one success); two-pointer on the unimodal expected-successes function.

2. Moorio Kart — forest of K farms (components with ≥2 nodes); count length-≥Y loops formed by stitching all K farms via K extra edges of length X; meet-in-the-middle DP.

3. Mowing Mischief — for each flower in the longest-antichain LIS layer, minimize the max-area rectangle pair; LIS + divide-&-conquer DP optimization.

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.