Спасибо за разбор

why are we taking ceil in problem A?

Does anyone have a solution to problem E through a segment tree?

222359696 I had somewhat similar thinking process in D, however, my way of calculation led to imprecise numbers where there were lots of digits. But why exactly? Test 4 failed because there were differences in the 17th tenth lol.

For problem G, let's say we want to find under what conditions it is optimal take the product of a subarray .

Suppose we have a prefix product equal to $$$p$$$ at index $$$i$$$ and we are considering joining this product to a $$$>1$$$ element at index $$$j > i$$$ to take the product. In the worst case, we have the array $$$A = [p, 1, ..., 1, 2]$$$ with $$$n - 2$$$ ones in between the first and last element.

For the product to be optimal: $$$2 * p > p + (n - 2) + 2 \Rightarrow p > n$$$, so the total product ($$$2 * p$$$) must be strictly bigger than $$$2n$$$ as mentioned in the tutorial.

For problem F, can someone please find the scenario where this submission is failing? 222376285

problem A ，why 2*c ？

Good problem and fast editorial, Thanks for this contest!

We can make the bound even better ( although not needed ) for problem G. We shall first exclude all prefix and suffix ones to get new array. If we include all elements of this new array , the answer is atleast P ( product of all elements ) — 2 * 10^5*10^9 ( here by answer I mean product(subarray(l,r)) — sum(subarray(l,r)) as we are maximizing it.). Which means it is atleast P — 2^48. Now any subarray other than this full array will have product at most P / 2. so answer for any subarray is atmost P / 2. Now , P — 2 ^ 48 >= P / 2 implies P >= 2 ^ 49. hence we can check if P >= 2 ^ 49 ( instead of 60 . )

Alternate thought process of Problem A:

WLOG assume, a<b (otherwise swap a and b) let m = (a+b)/2, now we need to pour water from vessel B to vessel A such that both vessel contain 'm' unit of water. We can only think in terms of vessel B (vessel A will be automatically handled). So we need to transfer (b-m) water from vessel B (to vessel A). Each time we can pour almost 'c' unit.

So ans = ceil ((b-m)/c)

My submission:222221006

Silly me has written a lazy segment tree for E.

problems were well balanced thank you for the contest

Editorial solution for problem G TLE on test 61

I'm new to CP. I used codeforces for 10 days, a few months ago, to improve my implementation skills. But the thing is, I can't solve questions like C (the gcd one). Since I'm new to cp, I wouldn't mind if I can't solve the D or above problems. I really want to learn how to solve math problems. Like it's so hard. I feel like it's totally different from my college-level math. Though they are all very basic math problems, I can't solve them on codeforces or codechef. I try to solve a math problem (div2/3 A) but when I look at the editorial, it's just only an equation. Can anyone suggest some resources to learn how to solve these gcd, prime numbers, combinatorics, kind of math problems on codeforces?? I'm gonna take cp seriously from now.

Thank you!

Thanks for the tutorial.

Another greedy solution for F https://codeforces.net/contest/1872/submission/222276481

222445465 does anyone know why i am getting runtime error in this code?

For G, there probably be a roughly prof: say we have a1(>1), 1, 1, 1,... (we have x ones), P1(products of remaining numbers), so if we left a1 the result will be a1 + x + P1, otherwise it's P1 * a1. Then a1+x+P1-P1*a1=(1-a1)*P1+a1+x, because P1 is large enough, and a1>1, a1+x+P1-P1*a1 will always < 0, so a1+x+P1 < P1*a1.

Why is there inconsistency in the rating change mentioned in friends standing and the friends rating change? My rating change displayed in the last column of friends standing and in friends rating change are different.

Interesting div.3 contest.

How to solve problem E if instead of finding XOR of elements we had to find sum?
Calculate the value of the bitwise XOR of the numbers ai for all indices i such that si=g
Here, instead of bitwise XOR, we had to calculate sum.

How to solve F if an animal was afraid of more than one animal?

1599 is like a clown. Please, give me one extra point༼ つ ◕_◕ ༽つ.

Wow, problem D has been explained amazing

Problem F can be solved using std::multiset. My solution is here

Simple Neat and Clean code for Codeforces Round 895 (Div. 3)

krishnash1355

Solutions:

Problem A : 1872A - Two Vessels Submission A : 222226952

Problem B : 1872B - The Corridor or There and Back Again Submission B : 222235441

Problem C : 1872C - Non-coprime Split Submission C : 222275700

Problem D : 1872D - Plus Minus Permutation Submission D : 222260066

Problem E : 1872E - Data Structures Fan Submission E : 222285746

I don't understand A. Why is it 2*c, why not c, 3c, 4c??

Lovely F :))

Really good problems, thanks authors

for problem E ,1e15 or 2^60 or 2^48 are very loose bounds .It seems to me that the solvers that passed the test cases didnot actually solve the problem.Nobody here has comeup with such bound .I actually want to understand the problem.

Why is sample test 3 for problem F correct?

5
2 1 1 1 1
9 8 1 1 1

With this output the money you get is 31, but if the output is:

The money is 32. What?

why my code is giving wrong output?

Submission Link Problem G

In problem F, the tutorial says "As each animal is feared by at least one other animal." But in the problem statement, it doesn't say this. It only says "Each animal is afraid of exactly one other animal." Therefore implying some animals may be feared by multiple animals, which would then contradict the tutorial's statement.

Could you please clarify which is correct?

I solved problem F using the same logic as the editorial but am getting a MLE, could someone explain what is the bottleneck in this code 265848420

Hello. I want to know why the upper bound can be $$$2n$$$ in problem G. Can anyone tell me?

.