🧠 Engineering Culture

AtCoder ABC452 A-D: From Festival Dates to Subsequence Counts, Dissected

AtCoder's Beginner Contest 452 packed 10,000+ coders into a 2-hour sprint across four problems. But problem D—with strings up to 200k chars—exposed how thin the line is between AC and TLE.

Dev Digest Apr 11, 2026 4 min read
AtCoder ABC452 problems A-D with Python code snippets and complexity graphs

⚡ Key Takeaways

  • ABC452 D risks O(n^2) in subseq check but often passes—audit complexities. 𝕏
  • Precompute sets turn C's existence queries into O(1) lookups. 𝕏
  • Problems build from O(1) to O(n m) with m=2e5, training real constraints. 𝕏
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#ABC452 #AtCoder #AtCoder ABC452 #Python CP #Python algorithms #competitive programming #sliding window #string subsequences

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Originally reported by dev.to

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