hashtable

I am trying to understand some things about jump tables and its relationship between a switch case statement. I was told that a jump table is a O(1) structure that the compiler generates which makes lookup of values essentially about as fast as you can get. However in some cases a Hashtable/Dictionary might be faster. I was also told this will only work if the switch case contains ordered data values. Can someone please confirm or deny this and explain what a jump table is, it's importance and the time complexity versus using a dictionary or hashtable. Thanks. A jump table is an abstract

The problem in general: I have a big 2d point space, sparsely populated with dots. Think of it as a big white canvas sprinkled with black dots. I have to iterate over and search through these dots a lot. The Canvas (point space) can be huge, bordering on the limits of int and its size is unknown before setting points in there. That brought me to the idea of hashing: Ideal: I need a hash function taking a 2D point, returning a unique uint32. So that no collisions can occur. You can assume that the number of dots on the Canvas is easily countable by uint32. IMPORTANT: It is impossible to know

I have often heard people talking about hashing and hash maps and hash tables. I wanted to know what they are and where you can best use them for. First you shoud maybe read this article . When you use lists and you are looking for a special item you normally have to iterate over the complete list. This is very expensive when you have large lists. A hashtable can be a lot faster, under best circumstances you will get the item you are looking for with only one access. How is it working? Like a dictionary ... when you are looking for the word "hashtable" in a dictionary, you are not starting

Can someone please shed some light on how popular languages like Python, Ruby implements hash tables internally for symbol lookup? Do they use the classic "array with linked-list" method, or use a balanced tree? I need a simple (fewer LOC) and fast method for indexing the symbols in a DSL written in C. Was wondering what others have found most efficient and practical. The classic "array of hash buckets" you mention is used in every implementation I've seen. One of the most educative versions is the hash implementation in the Tcl language, in file tcl/generic/tclHash.c . More than half of the

I read that hash tables in Haskell had performance issues (on the Haskell-Cafe in 2006 and Flying Frog Consultancy's blog in 2009), and since I like Haskell it worried me. That was a year ago, what is the status now (June 2010)? Has the "hash table problem" been fixed in GHC? 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

I am in need of a performance-oriented hash function implementation in C++ for a hash table that I will be coding. I looked around already and only found questions asking what's a good hash function "in general". I've considered CRC32 (but where to find good implementation?) and a few cryptography algorithms. My table, though, has very specific requirements. Here's what the table will be like: 100,000 items max 200,000 capacity (so the load is 0.5) hashing a 6-character string which is a part of English sentence examples: "become" "and he" ", not " The number one priority of my hash table is

I've always used dictionaries. I write in Python. R Samuel Klatchko A dictionary is a general concept that maps keys to values. There are many ways to implement such a mapping. A hashtable is a specific way to implement a dictionary. Besides hashtables, another common way to implement dictionaries is red-black trees . Each method has it's own pros and cons. A red-black tree can always perform a lookup in O(log N). A hashtable can perform a lookup in O(1) time although that can degrade to O(N) depending on the input. danben A dictionary is a data structure that maps keys to values. A hash table

I am using a hash table in JavaScript, and I want to show the values of the following in a hash table one -[1,10,5] two -[2] three -[3, 30, 300, etc.] I have found the following code. It works for the following data. one -[1] two -[2] three-[3] How do I assign one-[1,2] values to a hash table and how do I access it? <script type="text/javascript"> function Hash() { this.length = 0; this.items = new Array(); for (var i = 0; i < arguments.length; i += 2) { if (typeof(arguments[i + 1]) != 'undefined') { this.items[arguments[i]] = arguments[i + 1]; this.length++; } } this.removeItem = function(in