Below is a condensed “one-month crash plan” geared toward someone at ~1200–1300 CF level, aimed at quickly solidifying foundations and boosting problem-solving skills. The general idea is:

1. Focus on fundamentals and master them (because that’s what you’ll find in every style—USACO, IOI, CF).
2. Split your practice between OI-style problem-solving (deeper, more conceptual) and faster Codeforces-style contests (timed, speed + implementation).
3. Learn systematically (i.e., read theory / watch videos / do guided tasks from USACO Guide, CSES, or your “handbook”) and apply immediately by solving problems of the same topic.

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Overall Philosophy

• Consistency Over Quantity: You don’t need to solve 20 problems a day if they’re all trivial or if you burn out. Better to solve fewer (say 3–5 challenging ones per day) but with thorough thought.
• Active Learning: After you solve (or fail to solve) a problem, read the editorial (or solutions on discussion boards). Then re-implement the tricky part you learned. This cements knowledge.
• Mix OI-Style and CF-Style:
  • OI style (USACO/CSES) fosters deep thinking, analyzing bigger constraints, more creative solutions.
  • CF style fosters speed, experience with implementation details, and problem variety.
• Upsolving: If you do a CF round or pick from a virtual contest, upsolve at least the next 1–2 problems you couldn’t get in the contest timeframe.

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Proposed Weekly Structure

You have 4 weeks. Each week has an overarching theme or set of topics, combined with daily tasks.

Week 1: Build/Review Core Fundamentals

• Topics:

  • Basic graph theory: BFS, DFS, shortest paths in unweighted graphs, connected components.
  • Essential data structures: arrays, lists, stacks, queues, sets/maps, priority queues.
  • Simple dynamic programming (e.g., knapsack, coin change, LIS).
  • Sorting & searching, binary search usage.
  • Greedy strategies (interval scheduling, typical “sort by something, pick in order” problems).

• Daily Routine:

  1. 1–2 hours of reading/watching theory (USACO Guide Bronze/Silver or relevant sections from CSES Handbook).
  2. 2 hours of problem practice from CSES or USACO Guide on the day’s topic. Aim for a mixture of “easy-medium” to ensure you can quickly implement fundamentals.
  3. (Optional) 1 hour of a short timed practice or Codeforces Div3 style problem set. Focus on speed + correctness.

• Why: You need to be able to implement these fundamentals fast and reliably, since they appear in 80% of medium-level competitive programming tasks.

Week 2: Push into Intermediate-Level Topics & Speed

• Topics:

  • More advanced graph patterns (trees, tree traversals, possibly DS for LCA if time allows).
  • More DP patterns (DP on trees, path counting, bitmask DP if you’re feeling adventurous).
  • Two-pointer / sliding window techniques (common in CF).
  • Basic math / combinatorics knowledge (modular arithmetic, fast exponentiation, nCr).
  • Data structures expansions (Fenwick/BIT, Segment Trees for range queries if you’ve got the basics down).

• Daily Routine:

  1. Theory: Read or watch for ~1 hour from USACO Gold-level topics or the relevant CSES chapters.
  2. Practice: Spend ~2 hours on targeted medium-difficulty problems. The USACO Guide (Gold sections) + CSES problem set is excellent here.
  3. CF Timed: At least every other day, do a virtual contest (Div2 or Div3 CF round) under timed conditions. Even if you only do 2–3 problems in the time, the contest environment is crucial.
  4. Upsolve: Next day, revisit the unsolved problems from your virtual contest and learn from them.

• Why: This is the “meat” of typical advanced Bronze–Gold or Div2–Div3 range. You’re picking up more tools (trees, stronger DP, data structures) while also improving speed.

Week 3: Strengthen Problem-Solving Depth

• Topics:

  • More specialized data structures (Segment Tree advanced usage, lazy propagation, or Union-Find if not solid yet).
  • Additional advanced graph topics if relevant (topological sort, bipartite matching basics, shortest path in weighted graphs like Dijkstra).
  • More complex DP / combinatorial arguments.
  • If you handle these quickly, dabble in advanced math or more specialized structures.

• Daily Routine:

  1. Pick 1–2 advanced topics (say, DS + advanced DP) to read from the USACO Platinum or from typical advanced tutorials.
  2. Practice: 1–2 harder problems that specifically use the new concept. For instance, if you learned bipartite matching, solve a flow-based or matching-based problem.
  3. Codeforces: Do at least 1–2 virtual contests or actual contests each week. Keep timing yourself.
  4. Reflect & Summarize: Keep short notes on each new trick or approach.

• Why: After building strong intermediate fundamentals, you need to push your ceiling higher. This is where you expand your library of known solutions.

Week 4: Consolidation + Intensive Practice

• Focus: Putting it all together and addressing your weak spots.

  • Revisit any topics you still feel uncertain about. For instance, if you keep messing up segment trees or a certain class of DP, re-practice with a smaller subset of carefully chosen problems.
  • Continue with at least 2–3 timed contests (virtual or live) each week.
  • Ramp up the difficulty of the OI-style problems from USACO/CSES.

• Possible Schedule:

  1. Daily Problem Set: 3–5 problems mixing all the themes (graph, DP, data structure, geometry, etc.). Force yourself to see if you can solve them within 1–2 hours total.
  2. Editorial Review: The moment you realize you’re stuck or finish the problem, read editorial, re-implement anything that you find new or interesting.
  3. Flashcard Your Patterns: Make sure you can recall typical coding templates or logic quickly (segment tree structure, BFS for bipartite check, standard DP transitions, etc.).
  4. Mock OI: If you have time, pick a set of 2–3 OI-style “longer” problems (like USACO Gold/Platinum or from older IOI tasks) and give yourself 3–4 hours to solve them in a single block.

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Practical Tips & Mindset

1. Learn to Let Go: If a problem has you stuck for too long (e.g., 1–2 hours without real progress), it might be time to look at hints/editorials. The goal is to maximize learning, not to get stuck endlessly.
2. Quality Over Quantity: Especially for OI style. Focus on understanding the solution fully—why each step is needed, how the data structure or DP transitions are derived.
3. Coding Speed & Cleanliness: In Codeforces (and many OI contests), small implementation errors or inefficient coding hamper you. Train to code systematically, test on small custom examples.
4. Analyze Mistakes: Keep a log (digital or paper) of typical mistakes (indexing errors, off-by-one, forgetting to re-initialize arrays, etc.).
5. Mental Stamina: If you’re aiming for OI or USACO, you often need to handle 2–3 tough problems in one sitting. Practice longer sessions once or twice a week to build that stamina.
6. Balance: Don’t neglect your health. A short walk or exercise can refresh your mind better than more hours of dull practice.

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Should You Grind OI Style or Also Do Codeforces?

• Short Answer: Do both.
  • OI-Style (USACO, CSES, older IOI problems, etc.) grows your depth—bigger constraints, more creative problem statements, complex data structures, strong problem analysis.
  • Codeforces trains speed, quick pattern recognition, and frequent exposure to different problem types in a timed environment.
• If forced to choose for a one-month period, I’d still recommend you split at least 70% OI-style / 30% CF (or do a CF round 1–2 times a week). The synergy is strong: OI style solidifies concept mastery, CF rounds keep you nimble.

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Summary Plan

1. Week 1: Core fundamentals (basic DS, BFS/DFS, simple DP, greedy). Lots of practice on CSES + USACO Bronze/Silver + 1–2 CF sessions.
2. Week 2: Intermediate expansions (more advanced graph/DP, two-pointers, segment tree basics). Increase CF rounds to ~2–3 times a week.
3. Week 3: Advanced expansions (tree-specific DP, matching/flow if you can, advanced DS like Fenwicks/SegTrees with lazy). Continue short, timed CF (or other site) contests + upsolving.
4. Week 4: Consolidate, fill gaps, do more “mock OI” style sessions, final practice on known weak topics, keep up 2–3 CF or virtual contests.

If you follow this plan rigorously—focusing on concept mastery and frequent timed practice—your overall skills and rating should make a significant jump within a month. Good luck and stay consistent!