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Hash Maps

Hash Maps

Hash maps are a common data structure used to store key-value pairs for efficient retrieval. A value stored in a hash map is retrieved using the key under which it was stored.

# `states` is a Hash Map with state abbreviation keys and state name values. states = { 'TN': "Tennessee", 'CA': "California", 'NY': "New York", 'FL': "Florida" } west_coast_state = states['CA']

Hash map underlying data structure

Hash maps are built on top of an underlying array data structure using an indexing system.

Each index in the array can store one key-value pair. If the hash map is implemented using chaining for collision resolution, each index can store another data structure such as a linked list, which stores all values for multiple keys that hash to the same index.

Hash function

Hash map data structures use a hash function, which turns a key into an index within an underlying array. The hash function can be used to access an index when inserting a value or retrieving a value from a hash map.

hash map only one value

Each Hash Map key can be paired with only one value. However, different keys can be paired with the same value.

#This is a valid Hash Map where 2 keys share the same value correct_hash_map = { "a" : 1, "b" : 3, "c" : 1 } #This Hash Map is INVALID since a key cannot have more than 1 value incorrect_hash_map = { "a" : 1, "a" : 3, "b" : 2 }

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