标题：
通过率：	14.8%
难度：	中等

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

For example,

Given s = "the sky is blue",

return "blue is sky the".

Update (2015-02-12):

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

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.

 

本本题思路比较清晰，就是遇到空格就是停止然后开始跳空格，最后进行迭代操作，具体代码如下：

1 public class Solution { 2     public String reverseWords(String s) { 3            s = s.trim(); 4     return helper(s,0).toString(); 5          6     } 7     private StringBuilder helper(String s, int index) 8 { 9     if(index>=s.length())10         return new StringBuilder(); 11     StringBuilder cur = new StringBuilder();12     int lastIndex = index;13     while(index < s.length() && s.charAt(index)!=' ')14     {15         cur.append(s.charAt(index++));16     }17     while(index < s.length() && s.charAt(index)==' ')18         index++;19     if(lastIndex == 0)20         return helper(s,index).append(cur);21     return helper(s,index).append(cur).append(' ');22 }23 }