• stateless
• take place over TCP/IP
• Port 80

The CAP Theorem says that it’s impossible to build an implementation of read-write storage in an asynchronous network that satisfies all of the following three properties:

Exchange rate conversion(LeetCode 399)

Equations are given in the format A / B = k, where A and B are variables represented as strings, and k is a real number (floating point number). Given some queries, return the answers. If the answer does not exist, return -1.0.

Unique path is classic problem solving by dynamic programming. There are many follow-ups for this problem. So I’m writting this blog trying to do some summary and have a better understanding of this kind of problem.

Observer Pattern(other names as Publish/Subscribe, Model/View) is used to build a one-on-one or one-on-many relation between objects. When the ‘one’ object happens to change, other objects could get announcement and then make their own update. The object which happens to change is called subject, the objects which get announcement are called observer. There are no relationship between observers and we could easily add and delete observers without changing other observers. Thus system could be more flexible to extend.

• Maybe we are the way we are because of the people we are with, or we just pick the people we need. However it works, when you find each other, you should never let go.

• 做一只鸟，爱惜羽毛
• 遇见了解

Factory patterns are widely used in Software Development. There are three type of factory patterns. They are Simple Factory Pattern, Factory Pattern, Abstract Factory Pattern. We will introduce these three pattern.

Thread safe is the key point in multithreading area. The reasons for multithreading problems are mainly on that: 1. Sharing resource/data 2. more than one threads operate the same data/resource. So in order to solve this problem, we need some technique to make sure only one thread operate the sharing data at the same time. In java, synchronized key word could work as we expected. Now we try to figure out how thie key word works.