Dynamic Programming

Dynamic programming is a technique for solving problems with the following properties:

1. An instance is solved using the solutions for smaller instances.
2. The solution for a smaller instance might be needed multiple times.
3. The solutions to smaller instances are stored in a table, so that each smaller instance is solved only once.
4. Additional space is used to save time.

经典题目：

1. 买卖股票I II III IV