151. Reverse Words in a String

Given an input string, reverse the string word by word.

For example,
Given s = "the sky is blue",
return "blue is sky the".

Update (2015-02-12):
For C programmers: Try to solve it in-place in O(1) space.

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.

问题描述：给定一个输入字符串，逐词地将该字符串反转。

分析：单词是由一个非空格字符序列组成的。字符串的每个单词是由一个或多个空格隔开，用split()字符串分割函数将字符串根据空格分割，然后将结果存入字符串数组，最后从后往前循环字符串数组连接数组中的每个字符串即可，注意除了最后一个单词外，每个单词之间用一个空格连接。考虑以下两种情况：

（1）字符串首位包括空格，用trim()函数去掉字符串首位的空格；

（2）字符串的每个单词之间包含多个空格，用replaceAll("\\s+"," ")函数将多个空格替换成一个空格。

public class Solution {    public String reverseWords(String s) {        String s1 = "";        if(s.trim().length()==0)            return "";        String words[] = s.trim().replaceAll("\\s+"," ").split(" ");        for(int i=words.length-1;i>=0;i--){            s1 =s1+ words[i];            if(i!=0)                s1+=" ";              }        return s1;    }}