pavelthebest's blog

By pavelthebest, history, 3 months ago, In English

Sometimes I wonder, what implementation of a segment tree to use. Usually, I handwave that some will suit, and that works in most of the cases.

But today I decided to back up the choice with some data and I ran benchmarks against 4 implementations:

  • Simple recursive divide-and-conquer implementation
    Code
  • Optimized recursive divide-and-conquer, which does not descend into apriori useless branches
    Code
  • Non-recursive implementation (credits: https://codeforces.com/blog/entry/18051)
    Code
  • Fenwick Tree
    Code

All implementations are able to:

  • get(l, r): get sum on a segment (half-interval) $$$[l; r)$$$
  • add(i, x): add $$$x$$$ to the element by index $$$i$$$

Here are the results:

Note: I decided not to apply any addition-specific optimizations so that with minor modifications the data structures could be used for any supported operations.

I generated queries the following way:

  • Update: generate random index (rnd() % size) and number
  • Query: at first, generate random length (rnd() % size + 1), then generate a left border for that length

Benchmarking source code. Note that ideally you should disable frequency scaling, close any applications that might disrupt the benchmark (basically, the more you close — the better) and pin the benchmark process to a single CPU (core).

Plot-generating Python script

My benchmarking data in case you want to do some more plotting/comparing.

I compiled the benchmark with #pragma GCC optimize("O3") on GNU GCC 11.3.0, and ran it with the CPU fixed on 2.4 GHz, the process pinned on a single CPU core and the desktop environment closed.

This is probably my first useful contribution so any suggestions/improvements are welcome.

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By pavelthebest, history, 3 years ago, In English

This is racism, that in codeforces rating at the very bottom are located users with grey-to-black nicknames. This should be deleted: black and grey nicknames should be changed to another color (for example, light green).

#BLM

(disclaimer: this is, of course, a joke)

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