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My Data Structure: Bit-indexed Trie

Revision en12, by chromate00, 2022-09-01 18:53:40

This (quite sudden) post is about a data structure I have came up with in one day in bed, and this won't be a full series(I am yet a student, which means I don't have time to invent data structures all day and all night). Still, Thinking about this, I thought it would be a good idea to cover it on its own post. So here we are.


Concept

The traditional bit trie uses one leaf node for one number, and every leaf node has same depth. but about this, I thought — why? "Do we really have to use $$$32$$$ zeroes, just to represent a single zero? Heck no. There has to be a better way." And this is where I came up with this idea.

Instead of using the same old left-right child, let's use up to $$$l \leq depth$$$ children for one node. $$$l$$$ is the suffix part when each node represents a prefix. and then, we connect all prefixes that have exactly $$$1$$$ set bit after this prefix to this node. for example, under $$$1000_2$$$ comes $$$1100_2$$$, $$$1010_2$$$, $$$1001_2$$$. $$$0$$$ here has two meanings, before the last $$$1$$$ (LSB), it means a definite $$$0$$$ bit, while after it, it means there can be additional children under this node, but in this current node it represents the $$$0$$$ bit itself. This means that the node denoted as $$$1000_2$$$ has extra children ($$$1100_2$$$ and etc), but itself, it represents $$$1000_2$$$.


The Important Detail

At this moment, you should be wondering, how do we distinguish the node for the number $$$10000_2$$$ and the prefix $$$1\text{xxxx}_2$$$? They use the same node after all. My conclusion? You don't need to. To do this, you can just save the size (amount of elements) of the subtree. Now, let us denote the size of the subtree of prefix $$$S$$$ as $$$n(S)$$$. then $$$n(1\text{xxxx}_2) = n(11\text{xxx}_2) + n(101\text{xx}_2) + \ldots + n(10000_2)$$$ applies. So you can just traverse the child nodes one by one, and the rest is the number itself.

Tags trie, bitmask

History

 
 
 
 
Revisions
 
 
  Rev. Lang. By When Δ Comment
en30 English chromate00 2022-09-02 04:37:46 7 Tiny change: '(1)$, and he is correct. ' -> '(1)$, and they are correct. '
en29 English chromate00 2022-09-02 04:37:10 25 Tiny change: '9-02] and told me t' -> '9-02] and [user:Keewrem] told me t' (published)
en28 English chromate00 2022-09-02 04:36:38 5 Tiny change: '22-09-02] told me t' -> '22-09-02] and told me t' (saved to drafts)
en27 English chromate00 2022-09-02 03:33:02 0 (published)
en26 English chromate00 2022-09-02 03:32:43 208 (saved to drafts)
en25 English chromate00 2022-09-01 21:14:22 0 (published)
en24 English chromate00 2022-09-01 21:13:53 438
en23 English chromate00 2022-09-01 21:06:50 24 Tiny change: 'functions.' -> 'functions.\n\n-----\n\n### Summary'
en22 English chromate00 2022-09-01 21:05:33 375
en21 English chromate00 2022-09-01 20:59:10 2 Tiny change: ' BI-Trie">\n~~~~~\nvoi' -> ' BI-Trie">~~~~~\nvoi'
en20 English chromate00 2022-09-01 20:58:45 314
en19 English chromate00 2022-09-01 20:48:47 969
en18 English chromate00 2022-09-01 20:25:02 75
en17 English chromate00 2022-09-01 20:24:25 74
en16 English chromate00 2022-09-01 20:08:47 1082 Tiny change: '_2$. This toot node m' -> '_2$. This root node m'
en15 English chromate00 2022-09-01 19:07:28 198
en14 English chromate00 2022-09-01 19:04:59 69
en13 English chromate00 2022-09-01 19:02:49 452
en12 English chromate00 2022-09-01 18:53:40 134 Tiny change: '{xx}_2) + n(1001\text{x}_2) + n(10001_2) + n(10000' -> '{xx}_2) + \ldots + n(10000'
en11 English chromate00 2022-09-01 18:51:08 1 Tiny change: 'n(10000_2).' -> 'n(10000_2)$.'
en10 English chromate00 2022-09-01 18:50:59 279
en9 English chromate00 2022-09-01 18:45:29 38 Tiny change: '{xxxx}_2$?\n\n' -> '{xxxx}_2$? They use the same node after all.'
en8 English chromate00 2022-09-01 18:44:59 174
en7 English chromate00 2022-09-01 10:26:56 2 Tiny change: 'last $1$ (MSB), it me' -> 'last $1$ (LSB), it me'
en6 English chromate00 2022-09-01 10:26:17 120
en5 English chromate00 2022-09-01 10:23:13 14 Tiny change: 'se up to $32-l$ children' -> 'se up to $l \leq depth$ children'
en4 English chromate00 2022-09-01 10:22:12 533
en3 English chromate00 2022-09-01 07:41:44 307
en2 English chromate00 2022-09-01 03:11:46 123
en1 English chromate00 2022-09-01 01:52:09 427 Initial revision (saved to drafts)