Which Data Structure Is Used by Maps?


Heather Bennett

When it comes to storing data in programming, data structures play a crucial role. One commonly used data structure is the map. A map, also known as an associative array or dictionary, is a collection of key-value pairs that allows for efficient search and retrieval of values based on their associated keys.

Types of Maps

There are various types of maps available in different programming languages. Some examples include:

  • HashMap: This map implementation uses hash functions to store and retrieve key-value pairs efficiently. It provides constant-time average case complexity for insertion, deletion, and lookup operations.
  • TreeMap: In this map, the keys are sorted in a specific order (usually natural ordering or based on a comparator).

    The sorting allows for efficient range queries and operations like finding the smallest or largest key.

  • LinkedHashMap: This map maintains the insertion order of elements. It is implemented as a combination of a hash table and a linked list, providing fast access and iteration while preserving element order.

Data Structure Used by Maps

The underlying data structure used by maps depends on the implementation. HashMaps typically use an array of buckets, where each bucket can hold multiple key-value pairs.

When inserting a new element into the map, its hash code is computed to determine the bucket index where it should be placed. If multiple elements have the same hash code (known as hash collisions), they are usually stored as a linked list or a balanced binary tree within that bucket.

In contrast, TreeMaps utilize binary search trees (BSTs) as their underlying data structure. Each node in the BST contains a key-value pair and maintains its left and right child nodes. The keys are ordered in a way that allows for efficient searching and traversal of the tree.

Choosing the Right Map

The choice of map depends on the specific requirements of your program. If you need fast insertion, deletion, and lookup operations without any specific ordering, HashMaps are generally a good choice. However, if you require sorted keys or need to perform range queries efficiently, TreeMap might be more suitable.

LinkedHashMap can be useful when you need to preserve the order of insertion while maintaining efficient key-value retrieval.


In summary, maps are essential data structures for storing key-value pairs. The choice between different types of maps depends on factors like performance requirements and the need for specific ordering. Understanding the underlying data structure used by each map can help you make an informed decision when implementing maps in your programs.

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