151. Reverse Words in a String翻转一句话中的单词

Given an input string s, reverse the order of the words.

A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space.

Return a string of the words in reverse order concatenated by a single space.

Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces.

 

Example 1:

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

Example 2:

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

Example 3:

Input: s = "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.

Example 4:

Input: s = "  Bob    Loves  Alice   "
Output: "Alice Loves Bob"

思路：不用while (i < j),直接从最后一位开始倒贴就行了。这是一个好思路！

光是split就行了，不用再加toarray。

区别：toCharArray()是变成char array, split是变成string array
String[] words = s.split("\\s+");

 

字符串连接：明明就只有+和concat()，StringBuildr sb才用append()

 

class Solution {
    public String reverseWords(String s) {
        //cc
        if (s == null || s == "")
            return "";
        
        //分成words[]数组
        //光是split就行了，不用再变成array
        String[] words = s.split("\\s+");
        String result = "";
        
        //倒贴
        for(int i = words.length - 1; i > 0; i--) {
            //字符串连接明明就只有+和concat()，StringBuildr sb才用append()
            result += words[i];
            result += " ";
        }
        
        result += words[0];
        
        return result;
    }
}