Tree

* Binary Search Tree
- Search in BALANCED BST: O(logN)
- Insert and delete in BALANCED BST: O(logN)
- Obtain the parent node for a given node: O(logN)
- How to get maximal and minimal value in BST
- Output all the nodes SORTED in BST: O(N)
- Recursive algorithm associated

* Heap: Complete Binary Tree
- Implemented efficiently by an array due to its order and shape properties
- Insert, delete_min/max and delete: O(logN)
- Increase and decrease key: O(logN)
- Build heap: O(NlogN)
- Search in heap: O(N)

* Traversal
Preorder, DFS, postorder, in-order, and BFS

* Set
A set contains a sorted set of unique objects, which is usually implemented by BST.

* Examples
- Preorder traversal of BST without recursion
Stack is used to store the intermediate variables.
- Find the lowest ancestor of two nodes in one BST
The one with value between these two nodes would be the answer.
- Find the first K largest numbers or to find a subset of K numbers which sums up to at most T
Partial sort with one heap of K units.
- Find the K largest/smallest number in a heap of N elements with O(KlogK)/O(1). K is much less than N
- Construct a Huffman code and compute the sum of a large set of floating point number