hash table - Part of an article on https://dev.to/gitsushi/data-structures-5cpj

Part of an article on https://dev.to/gitsushi/data-structures-5cpj

Transcript

1. Hash Table
2. What does a hash table do ? A hash table is a data structure that uses hashing to implement mappings of key / value pairs.
3. What does a hash table do ? A simplistic diagram 1. Takes a key / value pair as input 2. Key goes through the hash function and returns an index 3. The pair is stored at that index hash function 1 { key: value }
4. What makes the hash table great ? • A hash function is irreversible. One cannot take the index and find the key. It only works one way. • A hash table is deterministic system. One gets the same result from the same input every time. • A hash table is very efficient. The time complexity in big O notation is O(1).
5. Notes • However it is possible for two different inputs to return the same result. This is called a collision. • Collisions are stored in a nested array. This method is called seperate chaining. • This is also why the time complexity worst case is O(n), n being the number of inputs.
6. Before we get to the code • Hash tables are included in most programming languages. This article is for a better understanding on how they work than a tutorial on how to implement one yourself. • In the following code example, we will implement an simple hash function. There are multiple ways to write them.
7. code review Hash Table
8. First comes the hash function. It takes a key of type string and an integer size as parameter.
9. The hashedkey is the sum of each character's code.
10. The size is the length of the array storing the key/value pairs. Thus hashedkey % size returns the index.
11. Then the hash table as an IIFE to immediately create the instance.
12. Fill the buckets array with Map objects to handle collisions.
13. The insert function invoking the hash function to get the index.
14. Then use the set method from Map object to store the key/value pair.
15. The remove function will save the value of the element to be removed with the get method of the Map object.
16. The delete method of Map will remove the element.
17. The search function returns the value with get method of Map with the appropriate index returned by the hash function.
18. The myBuckets function simply logs the buckets array.
19. All that is left to do is return the closures in an object.
20. Since we referenced hashTable to an Immediatly Invoked Function Expression, we can just invoke our methods.
21. Play around with the code on codepen by clicking the link below