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Codeforces Round #555 (Div. 3) Editorial
By vovuh, history, 6 years ago, In English

1157A - Reachable Numbers

Idea: BledDest

Tutorial
Solution

1157B - Long Number

Idea: BledDest

Tutorial
Solution

1157C1 - Increasing Subsequence (easy version)

Idea: MikeMirzayanov

Tutorial
Solution

1157C2 - Increasing Subsequence (hard version)

Idea: MikeMirzayanov

Tutorial
Solution

1157D - N Problems During K Days

Idea: MikeMirzayanov

Tutorial
Solution

1157E - Minimum Array

Idea: vovuh

Tutorial
Solution

1157F - Maximum Balanced Circle

Idea: MikeMirzayanov

Tutorial
Solution

1157G - Inverse of Rows and Columns

Idea: vovuh

This is the comment about the quadratic solution. Thank you so much for mentioning this fact, STommydx!

Tutorial
Solution
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Comments Comments (27)
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6 years ago, # |
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The editorial for Problem G looks like a little the editorial of Problem F

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    6 years ago, # ^ |
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    Thank you for mentioning, I just forgot to fix this place :)

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6 years ago, # |
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it was a greedy contest :D Good round by the way

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6 years ago, # |
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My solution problem D after contest(sad): 1)Find minimum first element with binary search 2) let's get maximum suffix, when we can add 1 for all numbers on segment, do it, while exist this is segment 3) end O(nLogn), and write easy

https://codeforces.net/contest/1157/submission/53393728

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6 years ago, # |
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1157D — N Problems During K Days can be solved simply by putting $$$1,2,\dots,k$$$ initially and then trying to put $$$(n-(k*(k+1)/2))/k$$$ elements in each, and then from reverse order adding as many elements in each position as possible, without considering special cases separately.

You can go through my submission for clear understanding.

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6 years ago, # |
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Anyone help me in finding the cause of TLE in Problem D in my solution.

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    6 years ago, # ^ |
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    "erase" for vector works in linear time of size of the whole vector

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6 years ago, # |
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This problem also has a solution like D:

https://www.codechef.com/SNCK1B19/problems/MAXPRODU

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6 years ago, # |
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Does anyone have a solution for problem E which does not involve STL structures, specifically without using multiset,set,map or multimap ?

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6 years ago, # |
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Problem D: "Then if nn != k — 1 or k = 1 then this answer is correct."

Any explanation for this ?

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6 years ago, # |
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For problem 1157c1, what if the input is

7 7 4 5 6 3 2 1

The solution code out puts 5 RRRRL But if I discard 7 and take the subsequence [4 5 6 3 2 1],it's possible to get a strictly increasing subsequence of size 6, right?

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6 years ago, # |
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When is the next div3?

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6 years ago, # |
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What's wrong with my solution for problem B? https://codeforces.net/contest/1157/submission/53566680 I am getting wrong answer on test case 7

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6 years ago, # |
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I solved D in a different way. Mine

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6 years ago, # |
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I'm kind of late, but problem D can be easily (more or less) solved by binary searching the first element, and then binary searching every other element as well, from left to right, so that the minimum possible sum is <= n and the maximum possible sum is >= n. My submission

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6 years ago, # |
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For the D problem, I just initialized array to 1,2,...,K then added (S — (K * (K + 1)) / 2) / N to every element in the array, and then just distributed (S — (K * (K + 1)) / 2) % N from the behind appropriately. Just wondering why there were so less submissions for this problem?

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6 years ago, # |
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How to solve problem Minimum Array using segment trees??

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    6 years ago, # ^ |
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    I solved with segment tree, so I will try to explain my solution:

    First we need to sort B array, to be able to find some index j for each $$$A_i$$$ such that $$$A_i + B_l \lt n$$$ for all $$$l \lt j$$$, and $$$A_i + B_r \ge n$$$ for all $$$r \ge j$$$. We'll have only one index j for each $$$A_i$$$, because $$$max(A) + max(B) < 2n$$$.

    After that we can divide B array in two parts and find the best among these greedly, using segment tree here to get minimum, and then updating the used element to not be taken more than once.

    Submission

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4 years ago, # |
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can anyone tell me mathematical proof of E i just wanted to know why finding greater element is optimal than finding lesser value element if n-a[i] is not found

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    4 years ago, # ^ |
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    It is because for any $$$k\geq n-a[i]$$$ and any $$$0\leq b < n-a[i]$$$, you will have $$$(a[i]+k) \mod n \leq a[i] + (n-1) \mod n < a[i] \leq a[i]+b < n$$$.

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4 years ago, # |
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In problem E first I used a sorted vector to store the elements of array b and used lower_bound+erase operations to find the appropriate element for the current a[i]. But it gave TLE on test 16. But when I used multiset instead of vector it passed all the tests. Can anyone explain why vector solution gave TLE?

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    3 years ago, # ^ |
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    This is because erase function in vector works in linear time(n), but in set or multiset, the data is already sorted so it works in constant time.o(1).

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2 years ago, # |
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i think i have better solution for D. We can search maximum value of c that sum of array(c, c + 1, c + 2 .... c + k) <= n; then we can run through this array from the end and greedily add 1 while the problem condition is being met. since we have to add a maximum of k units, we will be able to do this.

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