Hash Table vs STL Map
Hash table and STL map are very useful data structures in computer science. Here we will see the comparison between their properties as well as implementation. First, we will discuss their properties one by one, and then we will differentiate them based on their key characteristics.
Hash Table is a special type of data structure that stores data(key-value pair) in an associative manner and uses a hash function that maps a given value with a key to access the elements faster.
In the above diagram, keys are mapped to corresponding indices of the hash table using the hash function.
- As the access time in the hash table is O(1) (i.e., constant ), inserting, deleting, and looking up data can be done very fast.
- The hash table also performs well in the case of large datasets.
A Hash table is generally implemented by an array of linked lists where each node will store key-value pairs. A good hash function and collision resolution techniques like chaining are required for mapping the keys properly.
STL map is an associative container provided by the C++ STL library. It stores elements with key-value pairs but no two mapped values should have the same keys.
STL map containing key-value pairs
- A binary search tree can be implemented using the map where all key-value pairs will be in an ordered manner with searching time O(log n).
- Map implementation of the hash table is also possible with constant search time.
STL map is generally implemented using a red-black tree where insertion, deletion algorithm takes O(log n) time and O(1) for rebalancing.
|In the hash table, values are not in sorted order.||But in the STL map, values are in sorted order.|
|Hash table never allow null keys||It allows a null key.|
|Searching time is less in comparison to the STL map.||Here search time is O(log n)|
|It is mostly used for large data sets.||STL map is used for smaller data sets.|
|Hash table is thread-safe as it can be shared with many threads.||But the map is not thread-safe.|
1). What is the syntax of the C++ STL map?
map<datatype, datatype> map_name
2). What is the collision in the case of hashing?
A hashing collision occurs when the mapping for a given key returns an occupied slot in the hash table.
3). What are the collision resolution techniques?
Collision resolution is mainly done through chaining and rehashing till finding an unoccupied location in the hash table.
This article covered the comparison between Hash Table and STL Map from different perspectives. Having a good hold on these data structures is very important for cracking any coding round.
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