[LeetCode] 151. Reverse Words in a String

翻转字符串里的单词。题目即是题意。例子，

Example 1:

Input: "the sky is blue"
Output: "blue is sky the"

Example 2:

Input: "  hello world!  "
Output: "world! hello"
Explanation: Your reversed string should not contain leading or trailing spaces.

Example 3:

Input: "a good   example"
Output: "example good a"
Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string.

有两种corner case需要排除，一种是input前后多余的空格，一种是单词之间的多余空格。思路是先把input字符串分开成数组，再将数组reverse，最后将数组的每个元素拼接成字符串。

时间O(n)

空间O(n)

Java实现

 1 class Solution {
 2     public String reverseWords(String s) {
 3         // corner case
 4         if (s == null || s.length() == 0) {
 5             return s;
 6         }
 7 
 8         // normal case
 9         StringBuilder sb = new StringBuilder();
10         // trim 前后 skip 中间的回车 空格之类的东西
11         String[] words = s.trim().split("\\s+");
12         for (int i = words.length - 1; i >= 0; i--) {
13             sb.append(words[i] + " ");
14         }
15         return sb.toString().trim();
16     }
17 }

JavaScript实现

 1 /**
 2  * @param {string} s
 3  * @return {string}
 4  */
 5 var reverseWords = function (s) {
 6     return s
 7         .split(' ')               //create an array of words separated based by spaces
 8         .filter(string => string) //remove empty strings to take care of extra whitespace
 9         .reverse()                //reverse the array of words
10         .join(' ');               //join the words back together with spaces inbetween
11 };