21 June 2020

Codeforces Round #651 (Div. 2) Postmortem

What went well
  • Decently fast ABC (0:01, 0:10, 0:23).
What went wrong
  • Walled by D. I didn't recognize that binary search works because I didn't know how to verify that a subsequence with max less than or equal to a target value was doable in O(N).
  • I thought incorrectly (yet again) that O(N lg N) is too slow for N <= 10**6, so I tried something silly to find the minimum # subsequences of the form (01)+ or (10)+, when a straightforward O(N lg N) would have worked.
Where I got lucky
  • Gained rating!

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