LeetCode 151. Reverse Words in a String

原题链接在这里:https://leetcode.com/problems/reverse-words-in-a-string/

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".

题解:

把原有string s按照空格分开存入strArr中, 再从strArr尾部开始一个一个加到StringBuikder中即可.

Note:  1.这里学习了几个新的API, string.split(" ")可以按照空格把原有string分开但若是有连续空格比如"a  a"中间有两个空格,就会拆成[a,  , a], 中间的空格会保留。但若是用string.splict("\\s+")也是按照空格分开,但是上面连续两个空格时就不会额外拆出一个空格。

2. 若是string开头有空格,如" a", string.splict("\\s+")拆出的array长度为2, 也会包含空的string, strArr 会像["","a"]. 所以要像Simplify Path在加到StringBuikder前判定strArr[i].length()是否为0.

3.最后会多加一个 空格 在sb中,所以最后要用sb.deleteCharAt(sb.length()-1)消掉最后一个空格.

Time Complexity: O(s.length()).

Space: O(strArr.length).

AC Java:

 1 class Solution {
 2     public String reverseWords(String s) {
 3         if(s == null || s.length() == 0){
 4             return s;
 5         }
 6         
 7         String [] arr = s.trim().split("\\s+");
 8         StringBuilder sb = new StringBuilder();
 9         for(int i = arr.length-1; i>=0; i--){
10             sb.append(arr[i] + " ");
11         }
12         
13         sb.deleteCharAt(sb.length()-1);
14         return sb.toString();
15     }
16 }

跟上Reverse Words in a String IIReverse Words in a String III.

posted @ 2015-09-21 04:42  Dylan_Java_NYC  阅读(266)  评论(0编辑  收藏  举报