151. Reverse Words in a String-蒲公英云

151. Reverse Words in a String

Dear 丶 2022-06-11 07:23 267阅读 0赞

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;
    }
}