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Mixed Rounds

Mixed rounds are for breadth and retrieval, not first exposure.

Use them when you already know the basics of several areas and want to practice switching gears under light contest pressure.

Last reviewed against official follow-up pools: 2026-04-24

Who This Folder Is For

Use mixed rounds when:

  • you can already solve focused ladder problems in several topics
  • your bottleneck is recognition and switching, not syntax alone
  • you want a short review session or contest-style drill without opening a full contest archive first

Do not use this folder as the first place you learn a topic. Go through the corresponding topic page and ladder first.

Pack Contract

Each pack should say:

  • who it is for
  • what the entry gate is
  • what type of round it is
  • what topics are under test
  • how many problems it contains
  • how long one sitting should take
  • what refreshers are allowed
  • what the running rules are
  • how to debrief afterward
  • where to go back next if one slot exposed a weak topic

How To Run A Pack

Good mixed-round usage looks like this:

  1. learn the topic in topics/, then stabilize it in its ladder
  2. use a mixed round to test retrieval and switching
  3. go back to the weakest topic family afterward

Default operating loop:

  1. start each slot with an honest no-notes attempt
  2. if recognition is still fuzzy after about 10-15 minutes, allow one notebook or topic refresher
  3. if you are still blocked after about 25-30 minutes, log the missed recognition cue and move on
  4. after the full pack, only then read the stored note and code carefully

Recovery Doors

When one slot exposes a weak point, do not guess where to go next:

Minimal pack contract:

  • Who This Is For
  • Entry Gate
  • Pack Shape
  • Topics Under Test
  • Suggested Order
  • How To Run It
  • Allowed Refreshers
  • Debrief
  • Go Back Next

Starter Packs

If your bottleneck is... Start with
first retrieval session after the beginner route Stage 0 Review Pack 01
short-round shipping, anti-hack discipline, and clean CF-style debrief Codeforces Short Round 01
broad contest-core switching Contest Core Switching 01
one-machine-style banker prioritization plus implementation stability ICPC Breadth And Implementation 01
switching between graph modeling and DP state design Graphs And DP Switching 01
switching between string processing, modular reasoning, and counting Strings, Math, And Counting 01
switching across static, dynamic, offline, and greedy data-structure choices Data Structures And Offline 01
rooted-tree retrieval keeps drifting between ancestor, DP, and path-query views Trees And Queries 01
camp-style advanced switching across hard implementations Petrozavodsk / OpenCup Hard Mixed 01

Official Follow-Up Pools

Research snapshot: reviewed against official pages on 2026-04-24.

  • CSES Problem Set: best official follow-up pool when a pack reveals one weak core topic
  • Codeforces Problemset: best official follow-up pool when a short-round drill reveals one weak CF slot you want to replace immediately with another rep
  • USACO Training: good for slower, lesson-style follow-up after a mixed round exposes a concept gap
  • USACO Training Gateway: legacy training gateway if you want a second official progression path

Design Rules

  • mixed rounds should reinforce already-learned ideas, not introduce brand-new heavy material
  • each pack should mix topics on purpose instead of feeling like a random judge list
  • every pack should leave the learner with a clear “go back to this topic next” signal
  • one pack should usually fit in one sitting
  • allowed refreshers should be explicit so the drill stays honest and repeatable

Choose Your Next Pack

Bottleneck Time budget Start with If it breaks, go back to
first retrieval session after the beginner route 90-120 min Stage 0 Review Pack 01 Foundations ladders or BFS And DFS ladder
short-round shipping, anti-hack, and upsolve discipline 2-2.5 h Codeforces Short Round 01 Codeforces Playbook, Anti-Hack Workflow, Constructive ladder, or Prefix Constraints ladder
broad contest-core switching 2.5-3.5 h Contest Core Switching 01 the weakest corresponding ladder for the failed slot, then Problem Finder
banker-first ICPC breadth plus implementation reliability 3-4 h ICPC Breadth And Implementation 01 ICPC Playbook, Foundations ladders, Graphs ladders, or Segment Tree ladder
graph-modeling vs DP-state reset 3-4 h Graphs And DP Switching 01 Graph Modeling, Knapsack Family, or Digit DP
symbolic switching across strings, modular arithmetic, and counting 2.5-3.5 h Strings, Math, And Counting 01 KMP, Modular Arithmetic, or Counting Basics
data-structure choice keeps drifting between static, dynamic, ordered, and offline 3-4 h Data Structures And Offline 01 Sparse Table, Heaps And Ordered Sets, Offline Tricks, or Segment Tree
rooted-tree queries still feel like separate tricks instead of one family 3-4 h Trees And Queries 01 Trees, LCA, Tree DP, or HLD
advanced camp-style switching across decomposition, persistence, rollback, and DP optimization 4.5-6 h Petrozavodsk / OpenCup Hard Mixed 01 Centroid Decomposition, Persistent Data Structures, DSU Rollback, or CHT / Li Chao