Codeforces | Solutions to Codeforces Problems | Learning library

Here is the task: https://codeforces.com/problemset/problem/492/B And here is my code:

There are multiple approaches to solve the codeforces problem F. Consecutive Subsequence:

You are given an integer array of length 𝑛

You have to choose some subsequence of this array of maximum length such that this subsequence forms a increasing sequence of consecutive integers. In other words the required sequence should be equal to [𝑥,𝑥+1,…,𝑥+𝑘−1] for some value 𝑥 and length 𝑘.

Subsequence of an array can be obtained by erasing some (possibly zero) elements from the array. You can erase any elements, not necessarily going successively. The remaining elements preserve their order. For example, for the array [5,3,1,2,4] the following arrays are subsequences: [3], [5,3,1,2,4], [5,1,4], but the array [1,3] is not.

The Python code for one approach I tried that does not use dynamic programming is shown below. To avoid repetition, the if statement checks that the number one lower than the current number is not present in the array before because then it could be included to increase the subsequence's length.

I'm trying prove the correctness of my algorithm.
This is the problem in codeforces: https://codeforces.com/contest/1428/problem/C

Here's my code in C++ which was accepted:

In this programming problem, the input is an n×m integer matrix. Typically, n≈ 10⁵ and m ≈ 10. The official solution (1606D, Tutorial) is quite imperative: it involves some matrix manipulation, precomputation and aggregation. For fun, I took it as an STUArray implementation exercise.

I have managed to implement it using STUArray, but still the program takes way more memory than permitted (256MB). Even when run locally, the maximum resident set size is >400 MB. On profiling, reading from stdin seems to be dominating the memory footprint:

Functions readv and readv.readInt, responsible for parsing integers and saving them into a 2D list, are taking around 50-70 MB, as opposed to around 16 MB = (10⁶ integers) × (8 bytes per integer + 8 bytes per link).

Is there a hope I can get the total memory below 256 MB? I'm already using Text package for input. Maybe I should avoid lists altogether and directly read integers from stdin to the array. How can we do that? Or, is the issue elsewhere?

My two submissions for a programming problem differ in just one expression (where anchors is a nonempty list and (getIntegrals n) is a state monad):

Submission 1. replicateM (length anchors - 1) (getIntegrals n)

Submission 2. sequenceA $ const (getIntegrals n) <$> tail anchors

The two expressions' equivalence should be easy to see at compile time itself, I guess. And yet, comparatively the sequenceA one is slower, and more importantly, takes up >10x memory:

^{(with "Memory limit exceeded on test 4" error for the second entry, so it might be even worse).}

Why is it so?

It is becoming quite hard to predict which optimizations are automatic and which are not!

EDIT: As suggested, pasting Submission 1 code below. In this interactive problem, the 'server' has a hidden tree of size n. Our code's job is to find out that tree, with minimal number of queries of the form ? k. Loosely speaking, the server's response to ? k is the row corresponding to node k in the adjacency distance matrix of the tree. Our choices of k are: initially 1, and then a bunch of nodes obtained from getAnchors.

These are my answers for a codeforces problem and I don't know why the first snippet gives a wrong answer.

The second is accepted though.

I want to know if there is a problem with the judgment test cases because they seem to give the same output.

The problem says the following:

Given the boundaries of 2 intervals. Print the boundaries of their intersection.

Note: Boundaries mean the two ends of an interval which are the starting number and the ending number.

Input: Only one line contains two intervals [l1,r1], [l2,r2] where (1≤l1,l2,r1,r2≤109), (l1≤r1,l2≤r2).

It's guaranteed that l1≤r1 and l2≤r2.

Output: If there is an intersection between these 2 intervals print its boundaries , otherwise print -1.

Snippet 1

this is the problem enter link description here

the problem in function prime but it think it is true , and i can not find solution

i submit it in codeforces but it give me .Wrong answer on test 5
:-

the input :

I want to know why str += "A" and str = str + "A" have different performances.

In practice,