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Problems

USACO-Liam-1-vector_sort

Gym 667821

# Problem Original Rating Tries First AC Status
A Vanya and Fence 677A 800 1 2026-02-01 ✅
B Anton and Danik 734A 800 3 2026-01-31 ✅
C Translation 41A 800 1 2026-01-31 ✅
D Wrong Subtraction 977A 800 0 — —
E Tram 116A 800 0 — —
F Team 231A 800 1 2026-02-03 ✅
G Twins 160A 900 0 — —
H Chat room 58A 1000 2 — ❌ WA5
I Football 43A 1000 0 — —
J Present from Lena 118B 1000 0 — —
K The Smallest String Concatenation 632C 1700 1 2026-02-08 ✅
Tags (think first, then expand)
  • A: implementation
  • B: implementation, strings
  • C: implementation, strings
  • D: implementation
  • E: implementation
  • F: brute force, greedy
  • G: greedy, sortings
  • H: greedy, strings
  • I: strings
  • J: constructive algorithms, implementation
  • K: sortings, strings

USACO-Liam-2-custom_sorting

Gym 670674

# Problem Original Rating Tries First AC Status
A Showering 1999C 800 0 — —
B Parity Sort 1851B 800 1 2026-02-15 ✅
C Choose the Different Ones! 1927C 1000 4 2026-02-19 ✅
D Startup 2036B 800 0 — —
Tags (think first, then expand)
  • A: greedy, implementation
  • B: greedy, sortings, two pointers
  • C: brute force, greedy, math
  • D: greedy, sortings

USACO-Liam-3-set

Gym 673232

# Problem Original Rating Tries First AC Status
A ICPC Balloons 1703B 800 1 2026-03-01 ✅
B Distinct Split 1791D 1000 1 2026-03-01 ✅
Tags (think first, then expand)
  • A: data structures, implementation
  • B: brute force, greedy, strings

USACO-Liam-4-quick_power

Gym 675781

# Problem Original Rating Tries First AC Status
A Arpa's hard exam and Mehrdad's naive cheat 742A 1000 2 2026-03-05 ✅
B Filling the Grid 1228B 1400 0 — —
C Petr and a Combination Lock 1097B 1200 1 2026-03-08 ✅
D Jzzhu and Sequences 450B 1300 1 2026-03-08 ✅
Tags (think first, then expand)
  • A: implementation, math, number theory
  • B: implementation, math
  • C: bitmasks, brute force, dp
  • D: implementation, math

USACO-Liam-5-BinarySearch

Gym 683798

# Problem Original Rating Tries First AC Status
A Save More Mice 1593C 1000 3 2026-04-23 ✅
B Raspberries 1883C 1000 0 — —
C Cardboard for Pictures 1850E 1100 0 — —
D Target Practice 1873C 800 0 — —
E Removal of Unattractive Pairs 1907C 1200 0 — —
F Wooden Toy Festival 1840D 1400 0 — —
G Binary Deque 1692E 1200 0 — —
H Number of Pairs 1538C 1300 0 — —
I Money Trees 1873F 1300 1 2026-04-16 ✅
Tags (think first, then expand)
  • A: binary search, greedy
  • B: dp, math
  • C: binary search, geometry, implementation, math
  • D: implementation, math
  • E: constructive algorithms, greedy, math, strings
  • F: binary search, greedy, sortings
  • G: binary search, implementation, two pointers
  • H: binary search, data structures, math, two pointers
  • I: binary search, greedy, math, two pointers

USACO-Liam-6-TwoPointers

Gym 689999

# Problem Original Rating Tries First AC Status
A Prepend and Append 1791C 800 1 2026-05-14 ✅
B Books 279B 1400 1 2026-05-10 ✅
C Balanced Team 1133C 1200 1 2026-05-07 ✅
D Ternary String 1354B 1200 1 2026-05-07 ✅
E Blinds 38C 1400 2 2026-05-03 ✅
F They Are Everywhere 701C 1500 1 2026-05-10 ✅
G Approximating a Constant Range 602B 1400 0 — —
Tags (think first, then expand)
  • A: implementation, two pointers
  • B: binary search, brute force, implementation, two pointers
  • C: sortings, two pointers
  • D: binary search, dp, implementation, two pointers
  • E: brute force
  • F: binary search, strings, two pointers
  • G: dp, implementation, two pointers

USACO-Liam-7-Greedy

Gym 690622

# Problem Original Rating Tries First AC Status
A Eating Game 2200A 800 1 2026-05-17 ✅
B The 67th 6-7 Integer Problem 2218B 800 3 2026-05-10 ✅
C Lawn Mower 2194A 800 1 2026-05-17 ✅
D Reverse a Permutation 2193B 800 1 2026-05-17 ✅
E Replace and Sum 2193C 1000 1 2026-05-24 ✅
F Sorting Game 2190A 1200 1 2026-05-24 ✅
G Table with Numbers 2189A 800 1 2026-05-27 ✅
H The Curse of the Frog 2189B 1200 1 — ❌ WA1
I Seats 2188B 1000 2 2026-05-26 ✅
J Prefix Max 2185B 800 1 2026-05-27 ✅
Tags (think first, then expand)
  • A: greedy
  • B: greedy, math
  • C: greedy, math
  • D: greedy
  • E: data structures, greedy
  • F: constructive algorithms, games, greedy
  • G: greedy, implementation
  • H: constructive algorithms, greedy, math
  • I: greedy
  • J: greedy

USACO-Liam-8-Graph

Gym 716371

# Problem Original Rating Tries First AC Status
A Badge 1020B 1000 0 — —
B Forever Winter 1829F 1300 0 — —
C Ice Skating 217A 1200 0 — —
Tags (think first, then expand)
  • A: brute force, dfs and similar, graphs
  • B: dfs and similar, graphs, math
  • C: brute force, dfs and similar, dsu, graphs

OJ · Graph Basics

Four problems written for Liam after the graph lessons, on our judge (contest Graph Basics). Each has partial scoring over 20 / 30 / 50 points.

# Problem What it asks Read first
A P1201 Vertex Degrees degree of every vertex Graph Basics
B P1202 In and Out in- and out-degree in a directed graph Graph Basics
C P1203 Most Connected vertex with the largest degree, ties to the smaller index Graph Basics
D P1204 Adjacency List sorted neighbours of every vertex Graph Basics

AIO

Every AIO paper we worked through has its own page with statements summarised, the idea step by step, and the code from class: AIO overview.