Technology Fundamentals
Hash Table
Definition
A hash table (or hash map) is a data structure that implements an associative array abstract data type, a structure that can map keys to values. A hash table uses a hash function to compute an index, also called a hash code, into an array of buckets or slots, from which the desired value can be found.
Why It Matters
Hash tables provide extremely fast average-case lookup, insertion, and deletion of key-value pairs (O(1) time). They are one of the most useful and widely used data structures in all of programming.
Contextual Example
A contact list on a phone can be implemented as a hash table. The person's name (the key) is hashed to find an index where their phone number (the value) is stored. This makes looking up a number by name very fast.
Common Misunderstandings
- A "hash collision" occurs when two different keys hash to the same index. There are various strategies to handle collisions.
- The performance of a hash table depends heavily on having a good hash function that distributes keys evenly.