说明：  求单词个数的三种算法分析 用户任意输入一个字符串 ，求该字符串中包含的单词个数 ，其 中单词以空格分隔。这道题目难度合适，不用理解复杂的概念，纯粹的考察学生解决问题的能力，而且题目看似简单，学 生很有信心能够解决这个问题。每年讲解程序语言基础课或者程序设计高级时 ，都拿这道题目让学生做练习 ，但是学生做 的情况并不乐观 ，因此有必要总结一下 3 种经典解法 ，让初学者也能够体会到程序和算法的乐趣 ，让学生爱上学习。
(Find the number of words any of the three algorithms analyze user inputs a string, find the number of words contained in a string, in which words separated by spaces. This question is difficult to project the right, do not understand the complex concepts, students study the pure problem-solving skills, and the subject appears to be simple, the students are confident to solve this problem. Explain each programming language basic course or advanced programming, they all head to take the problem asks students to do exercises, but students do not optimistic, it is necessary to summarize the three kinds of classical solution, so that beginners can understand the procedures and algorithms fun for students to love learning.)