The complexity of creating a trie is O(W*L), where W is the number of words, and L is an average length of the word: you need to perform L lookups on the average for each of the W words in the set. Same goes for looking up words later: you perform L steps for each … Read more
Hashtable is the older class, and its use is generally discouraged. Perhaps they saw the need for a null key, and more importantly – null values, and added it in the HashMap implementation. HashMap is newer, and has more advanced capabilities, which are basically just an improvement on the Hashtable functionality. When HashMap was created, … Read more
Java’s Set and Map interfaces specify two very different collection types. A Set is just what it sounds like: a collection of distinct (non-equal) objects, with no other structure. A Map is, conceptually, also just what it sounds like: a mapping from a set of objects (the distinct keys) to a collection of objects (the … Read more
The language reference doesn’t make explicit guarantees about the performance of maps. There’s an implicit expectation that maps perform like you expect hash-tables to perform. I don’t see how a performance guarantee would avoid being either vaguely specified or inaccurate. Big-O complexity is a poor way to describe run-times for maps: practically speaking the actual … Read more
Object.keys will return all the keys in the object as a list, then use length to get the length. example: Object.keys(hash_table).length NOTE that this is ECMA 5 and may not be available in some browsers. see https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/keys for full document.
Try sdbm: hashAddress = 0; for (counter = 0; word[counter]!=’\0′; counter++){ hashAddress = word[counter] + (hashAddress << 6) + (hashAddress << 16) – hashAddress; } Or djb2: hashAddress = 5381; for (counter = 0; word[counter]!=’\0′; counter++){ hashAddress = ((hashAddress << 5) + hashAddress) + word[counter]; } Or Adler32: uint32_t adler32(const void *buf, size_t buflength) { … Read more
I experimented with both the # operator and table.getn(). I thought table.getn() would do what you wanted but as it turns out it’s returning the same value as #, namely 0. It appears that dictionaries insert nil placeholders as necessary. Looping over the keys and counting them seems like the only way to get the … Read more
Using the function above, you would do: var myHash = new Hash(‘one’,[1,10,5],’two’, [2], ‘three’,[3,30,300]); Of course, the following would also work: var myHash = {}; // New object myHash[‘one’] = [1,10,5]; myHash[‘two’] = [2]; myHash[‘three’] = [3, 30, 300]; since all objects in JavaScript are hash tables! It would, however, be harder to iterate over … Read more
C# 3 has a language extension called collection initializers which allow you to initialize the values of a collection in one statement. Here is an example using a Dictionary<,>: using System; using System.Collections.Generic; class Program { static void Main() { var dict = new Dictionary<string, int> { {“a”, 23}, {“b”, 45}, {“c”, 67}, {“d”, 89} … Read more
The problem was that the garbage collector is required to traverse mutable arrays of pointers (“boxed arrays”) looking for pointers to data that might be ready to deallocate. Boxed, mutable arrays are the main mechanism for implementing a hashtable, so that particular structure showed up the GC traversal issue. This is common to many languages. … Read more