7: Hash Tables

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Mar 9, 2021
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- 6.4: Discussion and Exercises
- 7.1: Time complexity and common uses of hash tables

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A hash table, or a hash map, is a data structure that associates keys with values. The primary operation it supports efficiently is a lookup: given a key (e.g. a person's name), find the corresponding value (e.g. that person's telephone number). It works by transforming the key using a hash function into a hash, a number that the hash table uses to locate the desired value. This hash maps directly to a bucket in the array of key/value pairs, hence the name hash map. The mapping method lets us directly access the storage location for any key/value pair.

Hash table<Element> Operations

make-hash-table(integer n): HashTable

Create a hash table with n buckets.

get-value(HashTable h, Comparable key): Element

Returns the value of the element for the given key. The key must be some comparable type.

set-value(HashTable h, Comparable key, Element new-value)

Sets the element of the array for the given key to be equal to new-value. The key must be some comparable type.

remove(HashTable h, Comparable key)

Remove the element for the given key from the hash table. The key must be some comparable type.

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