Conceptually, a merge sort works as follows: - - - wikipedia

1. Divide the unsorted list into n sublists, each containing 1 element (a list of 1 element is considered sorted).
2. Repeatedly merge sublists to produce new sorted sublists until there is only 1 sublist remaining. This will be the sorted list.

Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.

Given n, how many structurally unique BST’s (binary search trees) that store values 1…n?

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

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Given a binary tree, return the inorder traversal of its nodes’ values.