Problem description:

Given an array of non-negative integers, you are initially positioned at the first index of the array.

transaction:
fb: like, post
twitter: tweet, retweet
bitcoin: send money

Decentralize topology:
every node have whole copy.
51% of people have to approve/validate the new transaction.
the validation is done by miner, coin will be given to the 1st node that solve math problem.
Mining: verifying transactions by solving
transaction have queue up and group into block.

Problem description:

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

Problem description:

Given a binary search tree, write a function kthSmallest to find the kth smallest element in it.

Problem description:

Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.

Problem description:

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

Problem description:

Given a binary tree, determine if it is height-balanced.

Problem description:

Given two binary trees, write a function to check if they are the same or not.

Problem description:

Given two binary trees and imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while the others are not.

Problem description:

Invert a binary tree.