Reverse Words in a String 翻转一个字符串里的单词顺序 @LeetCode

LeetCode新题，可是比較简单，直接用栈就可以

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.

public class Solution {
    public String reverseWords(String s) {
        if(s.length() == 0) {
            return s;
        }
        Stack<String> stack = new Stack<String>();
        String[] ss = s.split("\s+");
        for(String word : ss) {
            stack.push(word);
        }
        StringBuilder sb = new StringBuilder();
        while(!stack.isEmpty()) {
            sb.append(stack.pop()).append(" ");
        }
        return sb.toString().trim();
    }
}