151. Reverse Words in a String

class Solution {
          public String reverseWords(String s) {
         StringBuffer ans = new StringBuffer("");
         StringBuffer res = new StringBuffer("");
         for(int i = 0 ;i< s.length() ;i++) {
             while(i< s.length()&&s.charAt(i)==' ')
                 i++;                //找到i所对应的字符不是" "
             StringBuffer temp = new StringBuffer("");        //用stringBuffer 效率高 用string就超时了
             while(i< s.length()&&s.charAt(i)!=' ') {
                 temp.insert(0, s.charAt(i)) ;
                 i++;
             }
             res.append( temp);res.append(" ");}
             int x = res.length()-1;
             while(x>= 0&&res.charAt(x)==' ') {                   //多加了几个空格 这里倒数找出非空格的位置 然后继续
                 x--;
             }
             while(x>= 0) {
                 ans.append(res.charAt(x));
                 x--;
             }

         return ans.toString();
        }
    }