Hashing is some kind of data structure used to store many data using mapping and the function called Hash function. The Hash function is used to store a value in the map provided that the user gives the key to that value.
Hash function's format: Hash(key) → index
Supposed we want to make a phonebook using the Hashing. The data that we store are phone numbers, these are the values that the Hashtable will later commit into memory. Say that we want to store Bob's phone number into the phonebook's index number 1, then we would write the Hash s function as such: " Hash(Bob) → 1 ". In this case, Bob is the key that can only be used to access his index in the mapping.
Hashing is almost like Linked List. The difference is that we can store multiple data into the same index, which we call the Hash Chain. Once we have the key and the index, then it is not very complicated to find somebody else's phone numbers even though it is stored in the same index as Bob here. As you can see in the picture below.
Image source: geeksforgeeks.org
The vertical white boxes containing the numbers 0-5 is what we call the Hashtable, while the horizontal colored boxes are what we call Hash Chain.
How is Hashing utilized in the current Blockchain technology?
In Blockchain, every block has a hash of the previous block. The previous block of our current block is called as the parent block.
According to a Blockchain developer, every block in the Blockchain has a hash of the previous block. If we change any data in the current block, the hash of the block will be changed. This will affect the current block, because the current block has the address of the previous block. They are interconnected to each other. In other words, we have to change the data in the current block, then we also have to change the data in our parent block. (note: current block is also called present block)
Binary Tree
A Binary Tree is a special type of tree in which every node or vertex has up to 2 child nodes. The starting node is called the root node. There are 2 terms to refer to child nodes (corresponding to which side of the node it is branching to): the left child node & the right child node. The nodes without any child node branching from it are called the leaf nodes.
Binary Trees can be represented in 2 ways: using arrays or using Linked Lists.
Types of Binary Trees:
1. Full Binary Tree / Proper Binary Tree / 2-tree: a tree in which all the node has exactly two children, except for the leaf nodes.
2. Complete Binary Tree: a binary tree in which at every level, except possibly the last, has to be filled and all nodes are as far left as possible.
