Contest Strategy

Contest Strategy — Codeforces Div 2

Time Allocation (2h for Div 2)

Phase	Time	Problems	Goal
Read & Categorize	First 5 min	All A,B,C,D	Decide which to skip
Solve A	5-15 min	A	100%
Solve B	10-25 min	B	100%
Solve C	30-45 min	C	Target
Solve D	30-40 min	D	If time remains
Stress test / Hack	Last 10 min	A,B	Avoid stupid fails

The Order of Operations

0️⃣ Before Contest

• Set up template with boilerplate already in editor
• Have fast I/O ready
• No distractions, good chair, water

1️⃣ Read ALL Problems First (5 min)

Skim through A,B,C,D — note: - What's the input/output format? - What's the constraint range? (n ≤ 20 → bitmask/DP, n ≤ 2000 → O(n²), n ≤ 2e5 → O(n log n)) - Does it smell like a known pattern? (XOR, parity, gcd, constructive) - Which problem looks most accessible after A?

2️⃣ Solve A (5-15 min)

If you can't solve A in 15 min, you're overcomplicating it. Read again, simplify.

3️⃣ Solve B (10-25 min)

B is usually greedy or constructive after a bit of reasoning. - If stuck >20 min on B, read C — sometimes B is harder than C for you.

4️⃣ Solve C (30-45 min)

This is where the real fight happens. C is the rating gatekeeper. - 1200-1400 rating C: binary search, math, DP, graphs - If nothing >30 min → read editorial after contest, don't waste more - The 30-min rule: If no concrete progress in 30 min, write down what you tried, submit brute-force if applicable, move to D

5️⃣ Solve D (if time)

D is usually a data structure / combinatorial problem (1400-1700). - If you're unrated/new, D is bonus — don't sacrifice C for D

Attack Patterns by Problem Type

"Implementation" problems (A, easy B)

• Write the brute-force translation directly
• Test on sample, submit immediately

"Math" problems

• Try small examples manually, find pattern
• Test edge cases: n=1, n=2, all zeros, all equals, max values
• Check parity, modulo, gcd

"Greedy" problems

• "What's the optimal choice at each step?"
• Prove with exchange argument: "If optimal solution does NOT pick X, swapping gives better"
• Try sorting and processing in some order

"Binary search on answer" problems

• "What's the minimum X such that condition holds?"
• Can you write check(X) that returns true/false?
• If yes, is check monotonic? (true for X≥something, false otherwise)

"Graph" problems

• Build graph from description (not given explicitly)
• Check if implicit graph (grid, functional, complement)
• Consider: is it a tree? Bipartite? DAG?

"DP" problems

• State: what changes between subproblems?
• Transition: how do I go from smaller to larger?
• If 2D, can I reduce to 1D?
• Check for segment tree optimization

Common Mistakes Checklist

Before submitting ANY solution: - [ ] Have I overflowed? (Use int64 for sums/multiplications) - [ ] Are array indices zero or one-based? - [ ] Have I handled n=1 / empty input? - [ ] Have I handled modulo correctly? (negative results?) - [ ] Is my DP initialized correctly? (INF for min, 0 for count) - [ ] Does the sample pass? - [ ] Can I come up with a custom edge case?

After failing pretest / Wrong Answer: 1. Re-read the problem statement — did I misread? 2. Check for off-by-one in loops 3. Add debug output for edge cases 4. If still stuck, move on and review later

Mental Game

• Stay calm — panic kills reasoning
• One problem at a time — don't think about C while solving B
• Skip and come back — sometimes the insight hits during another problem
• Read editorial after every contest — for every problem you didn't solve, write down the one-sentence insight
• Practice virtual contests — simulate contest conditions weekly
• Rate is just a number — the learning is in the process, not the number

○ Mark as completed