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Hi Codeforces,
In problem "Kefa and Dishes" (580D div 2), statements said that: "It is guaranteed that there are no such pairs of indexes i and j (1 ≤ i < j ≤ k), that xi = xj and yi = yj."
But in the 5th test case:
7 4 3 2 6 13 5 7 1 9 6 1 15 2 5 3 6 4 8
It's easy to see that x1 = x3. Was this test case invalid?
I think it's not a contradiction. Although it is x1 = x3, it doesn't mean "xi = xj and yi = yj" if y1 is not equal to y3. It means it should be (xi, yi) ≠ (xj, yj). It's just a coincidence but in yesterday's ACM-ICPC style contest I did exactly this type of misreading and I got 8 Wrong Answers.