leetcode------Reverse Words in a String

标题：	Reverse Words in a String
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.

click to show clarification.

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：

public class Solution {
    public String reverseWords(String s) {
           s = s.trim();
    return helper(s,0).toString();
        
    }
    private StringBuilder helper(String s, int index)
{
    if(index>=s.length())
        return new StringBuilder(); 
    StringBuilder cur = new StringBuilder();
    int lastIndex = index;
    while(index < s.length() && s.charAt(index)!=' ')
    {
        cur.append(s.charAt(index++));
    }
    while(index < s.length() && s.charAt(index)==' ')
        index++;
    if(lastIndex == 0)
        return helper(s,index).append(cur);
    return helper(s,index).append(cur).append(' ');
}
}