leetcode_Reverse Words in a String

描述：

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.

思路：

1.trim（）+去除串内多余的空格

2.将串内每个单词反转

3.将整个句子反转

代码：

public String reverseWords(String s) {
		s=s.trim();
		if(!s.equals(""))
		{
			char arr[]=s.toCharArray();
			int index=1;
			for(int i=1;i<arr.length;i++)
			{
				if(arr[i-1]==arr[i]&&arr[i]==' ')
					continue;
				else
					arr[index++]=arr[i];
				
			}
			s=new String(arr,0,index);
		}else {
			return "";
		}
		StringBuilder sBuilder=new StringBuilder(s);
		char ch;
		int i=0,j=s.length()-1;
		int start=0,end=0;
		for(i=0;i<sBuilder.length();i++)
		{
			start=i;
			while(sBuilder.charAt(i)!=' '&&i!=j)
				i++;
			end=i;
			if(end!=j)
				end--;
			while(start<end)
			{
				ch=sBuilder.charAt(start);
				sBuilder.setCharAt(start, sBuilder.charAt(end));
				sBuilder.setCharAt(end, ch);
				start++;
				end--;
			}
		}
		sBuilder.reverse();
        return sBuilder.toString();
    }