在本章，我们将看到 Java 程序的基本组成部分，并体会到在 Java 中（几乎）一切都是对象。

面向对象程序设计（Object-oriented Programming，OOP），本章内容以了解 OOP 为主。

Given s1, s2, s3, find whether s3 is formed by the interleaving of s1 and s2.

The longest common subsequence (LCS) problem is the problem of finding the longest subsequence common to all sequences in a set of sequences (often just two sequences). It differs from problems of finding common substrings: unlike substrings, subsequences are not required to occupy consecutive positions within the original sequences. The longest common subsequence problem is a classic computer science problem, the basis of data comparison programs such as the diff utility, and has applications in bioinformatics. It is also widely used by revision control systems such as Git for reconciling multiple changes made to a revision-controlled collection of files. - - - - wikipedia

In computer science, the longest common substring problem is to find the longest string (or strings) that is a substring (or are substrings) of two or more strings.- - - - wikipedia