LeetCode-Reverse Words in a String

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

For example,
Given s = "the sky is blue",
return "blue is sky the".

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.

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Solution:

public class Solution {
    public String reverseWords(String s) {
        s = s.trim();

        StringBuffer buff = new StringBuffer();
        int start = s.length()-1;
        while (start>=0){
            //Search the next work.
            int end = start;
            while (end>=0 && s.charAt(end)!=' ') end--;
            String word = s.substring(end+1,start+1);
            buff.append(word);
            if (end>0) buff.append(" ");

            //skip all the following spaces.
            while (end>=0 && s.charAt(end)==' ') end--;
            start = end;
        }

        return buff.toString();
    }
}