Hash Table 2

A Hash Table can map key to value for highly efficient lookup. 
A Hash Table uses a  hash function to compute an index into an array of buckets or slots, from which the correct value can be found.

[1]
[1] Image from Wikipedia, A small phone book as a hash table.

The goal of Hash Table is,

Keys are uniformly distributed in it, regardless of the sequence.
It supports insert, remove and find operations.
Each operation has better time complexity than O(log n).
Then in the next post, the method of  Hashing will be introduced to use on the Hash Table.