Reverse Words in a String leetcode java

题目：

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.

题解：

一个用了java的s.split(" ")，按空格分隔。

然后调用了系统函数：Collections.reverse(list);把list顺序调换了。

最后再把结果存成数组即可。

代码如下：

 1    public static String reverseWords(String s) {
 2         if(s==null||s.length()==0)
 3             return s;
 4         String [] result = s.split(" ");
 5         if(result==null||result.length==0)
 6             return "";
 7             
 8         ArrayList<String> list = new ArrayList<String>();
 9         
         for(int i = 0; i<result.length;i++){
             if(!result[i].isEmpty())
                 list.add(result[i]);
         }
         Collections.reverse(list);
         
         String ans = new String();
         for(int i = 0; i<list.size()-1;i++){
             ans += list.get(i)+" ";
         }
         ans +=list.get(list.size()-1);
         return ans;
     }