问题描述：

Given an input string, reverse the string word by word.

For example,
Given s = "

the sky is blue

blue is sky the

Update (2015-02-12):
For C programmers: Try to solve it in-place in O(1) space.

click to show clarification.

• What constitutes a word?
  A sequence of non-space characters constitutes a word.
• Could the input string contain leading or trailing spaces?
  Yes. However, your reversed string should not contain leading or trailing spaces.
• How about multiple spaces between two words?
  Reduce them to a single space in the reversed string.

原问题链接：https://leetcode.com/problems/reverse-words-in-a-string/

问题分析

　　这个问题的思路其实比较简单，因为它只是要把一个字符串里所有非空格的词语顺序给倒过来。那么我们就有这么一个基本的思路，首先将这个串按照空格给划分成多个非空的字符串。然后从后往前将字符串加入到一个StringBuilder中。最后去除两头的空格。当然，问题的要求里提到每个词语之间要有一个空格作为间隔，在实现的时候要注意这一点。

　　详细的代码实现如下：

public class Solution {
public String reverseWords(String s) {
String[] words = s.split("\\s+");
StringBuilder builder = new StringBuilder();
for(int i = words.length - 1; i >= 0; i--) builder.append(words[i] + " ");
return builder.toString().trim();
}
}