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Hash Maps: Conceptual
Review

We’ve learned together what a hash map is and how to create one. Let’s go over the concepts presented in this lesson.

A hash map is:

  • Built on top of an array using a special indexing system.
  • A key-value storage with fast assignments and lookup.
  • A table that represents a map from a set of keys to a set of values.

Hash maps accomplish all this by using a hash function, which turns a key into an index into the underlying array.

A hash collision is when a hash function returns the same index for two different keys.

There are different hash collision strategies. Two important ones are separate chaining, where each array index points to a different data structure, and open addressing, where a collision triggers a probing sequence to find where to store the value for a given key.

Instructions

What makes good data to save into a hash map? Can you think of instances where a hash map would help you solve a problem faster?

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