### galen_colin's blog

By galen_colin, 5 months ago, A1
A2
B
C
D
E

Some notes/backstory about the round in general:

• Sorry about the mistake in C! I hope it didn't affect you too much, if at all. You can blame this on my bad organization — a tester did actually catch this mistake, but somehow I forgot to correct it.
• The only tester feedback I received besides corrections was to swap the problems C and D. Based on the solve counts, I guess it worked out.
• A lot of people received WA17 or WA20 on D because of not making the default values in the array small enough. With $0$ as the default, you'd get WA17. Others, who used $-10^9$ or $-10^{10}$, got WA20. I actually made this mistake myself, and my brute-force didn't catch it because it only seemed to happen with large enough $n, k$.
• I was skeptical about placing E at the end because of how simple the solution was, but that seems like it was a good choice now.
• I understand criticism about the problems being too "standard" — in fact, I'm not really proud of having a problem like D, but I thought it was necessary for balance (turns out it wasn't anyway). At the very least, they could serve to teach people new algorithms. Tutorial of Testing Round #XVII Comments (5)
 » There is another solution for 102646A2 - Product of Triples (Hard Version)Iterate $x$ over all numbers from $[1,n]$For each number $x$, fix $i$ to be one of the divisors of the number $x$.Calculate $y$ = $x/i$, now iterate $z$ over all divisors of $y$. The three numbers would be $i$, $z$, $y/z$. Just check for the $a≤b≤c$ and count them !
 » Can someone explain task C? Explaining the output of the Sample TC is enough!
 » galen_colincan any one tell me why WA in this problem https://codeforces.com/gym/102646/problem/E my code ---> https://ideone.com/yB1W29 my idea is to search about sccs inside the graph then remove all edges from this scc and so on till remains k edges
•  » » The entire input graph is already strongly connected. So removing edges from this isn't guaranteed to work, and is essentially equivalent to removing $m - k$ random edges, which has no guarantee of producing the maximum number of SCCs.
•  » » » Yes I got it Thank you so much That Was clear