Hash tables are O(1) average and amortized case complexity, however it suffers from O(n) worst case time complexity. [And I think this is where your confusion is] Hash tables suffer from O(n) worst time complexity due to two reasons: If too many elements were hashed into the same key: looking inside this key may take … Read more
Usually hashes wouldn’t do sums, otherwise stop and pots will have the same hash. and you wouldn’t limit it to the first n characters because otherwise house and houses would have the same hash. Generally hashs take values and multiply it by a prime number (makes it more likely to generate unique hashes) So you … Read more
Use JavaScript objects as associative arrays. Associative Array: In simple words associative arrays use Strings instead of Integer numbers as index. Create an object with var dictionary = {}; JavaScript allows you to add properties to objects by using the following syntax: Object.yourProperty = value; An alternate syntax for the same is: Object[“yourProperty”] = value; … Read more
An easy, correct way to implement __hash__() is to use a key tuple. It won’t be as fast as a specialized hash, but if you need that then you should probably implement the type in C. Here’s an example of using a key for hash and equality: class A: def __key(self): return (self.attr_a, self.attr_b, self.attr_c) … Read more
Here is a class for a bidirectional dict, inspired by Finding key from value in Python dictionary and modified to allow the following 2) and 3). Note that : The inverse directory bd.inverse auto-updates itself when the standard dict bd is modified. The inverse directory bd.inverse[value] is always a list of key such that bd[key] … Read more
You have two variables here, m and n, where m is the length of the input and n is the number of items in the hash. The O(1) lookup performance claim makes at least two assumptions: Your objects can be equality compared in O(1) time. There will be few hash collisions. If your objects are … Read more
Bash 4 Bash 4 natively supports this feature. Make sure your script’s hashbang is #!/usr/bin/env bash or #!/bin/bash so you don’t end up using sh. Make sure you’re either executing your script directly, or execute script with bash script. (Not actually executing a Bash script with Bash does happen, and will be really confusing!) You … Read more
I’ve had nice results with djb2 by Dan Bernstein. unsigned long hash(unsigned char *str) { unsigned long hash = 5381; int c; while (c = *str++) hash = ((hash << 5) + hash) + c; /* hash * 33 + c */ return hash; }
Here’s an explanation in layman’s terms. Let’s assume you want to fill up a library with books and not just stuff them in there, but you want to be able to easily find them again when you need them. So, you decide that if the person that wants to read a book knows the title … Read more
What are the differences between a HashMap and a Hashtable in Java?