Reverse Words in a String leetcode java

題目：

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.

 

題解：

 一個用了java的s.split(" ")，按空格分隔。

然後呼叫了系統函式：Collections.reverse(list);把list順序調換了。

最後再把結果存成陣列即可。

程式碼如下：

 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         
10         for(int i = 0; i<result.length;i++){
11             if(!result[i].isEmpty())
12                 list.add(result[i]);
13         }
14         Collections.reverse(list);
15         
16         String ans = new String();
17         for(int i = 0; i<list.size()-1;i++){
18             ans += list.get(i)+" ";
19         }
20         ans +=list.get(list.size()-1);
21         return ans;
22     }