us
apv-median
us | apv-median | |
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2 | 1 | |
55 | 1 | |
- | - | |
1.5 | 0.0 | |
4 months ago | about 2 years ago | |
Go | C | |
MIT License | MIT License |
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us
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Ask HN: What are some 'cool' but obscure data structures you know about?
It might be easier to think about it as a stack, rather than a tree. Each element of the stack represents a subtree -- a perfect binary tree. If you ever have two subtrees of height k, you merge them together into one subtree of height k+1. Your stack might already have another subtree of height k+1; if so, you repeat the process, until there's at most one subtree of each height.
This process is isomorphic to binary addition. Worked example: let's start with a single leaf, i.e. a subtree of height 0. Then we "add" another leaf; since we now have a pair of two equally-sized leaves, we merge them into one subtree of height 1. Then we add a third leaf; now this one doesn't have a sibling to merge with, so we just keep it. Now our "stack" contains two subtrees: one of height 1, and one of height 0.
Now the isomorphism: we start with the binary integer 1, i.e. a single bit at index 0. We add another 1 to it, and the 1s "merge" into a single 1 bit at index 1. Then we add another 1, resulting in two 1 bits at different indices: 11. If we add one more bit, we'll get 100; likewise, if we add another leaf to our BNT, we'll get a single subtree of height 2. Thus, the binary representation of the number of leaves "encodes" the structure of the BNT.
This isomorphism allows you to do some neat tricks, like calculating the size of a Merkle proof in 3 asm instructions. There's some code here if that helps: https://github.com/lukechampine/us/blob/master/merkle/stack....
You could also check out section 5.1 of the BLAKE3 paper: https://github.com/BLAKE3-team/BLAKE3-specs/blob/master/blak...
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My proposal to the Foundation: add first-class S3 provider support
This isn't what I'm asking for - I don't care if it's baked into us, exists as a backend for minio, uses PseudoKV https://github.com/lukechampine/us/issues/67, or whatever the case may be. I see no value in sending any third party my private data in an unencrypted form (uploading to your server, even if over HTTPS, you got my data).
apv-median
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Ask HN: What are some 'cool' but obscure data structures you know about?
An alternative streaming method due to Arandjelović, Pham, Venkatesh based on maximum entropy: https://ieeexplore.ieee.org/document/6971097 and implementation in C: https://github.com/dressipi/apv-median
What are some alternatives?
lnd - Lightning Network Daemon ⚡️
rpart - Recursive Partitioning and Regression Trees
ego - EGraphs in OCaml
Caffeine - A high performance caching library for Java
swift - the multiparty transport protocol (aka "TCP with swarming" or "BitTorrent at the transport layer")
RVS_Generic_Swift_Toolbox - A Collection Of Various Swift Tools, Like Extensions and Utilities
pvfmm - A parallel kernel-independent FMM library for particle and volume potentials
t-digest - A new data structure for accurate on-line accumulation of rank-based statistics such as quantiles and trimmed means
gring - Golang circular linked list with array backend
clojure - The Clojure programming language
ctrie-java - Java implementation of a concurrent trie
FusionCache - FusionCache is an easy to use, fast and robust cache with advanced resiliency features and an optional distributed 2nd level.