151. Reverse Words in a String

Question

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

Example:

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

Thinking:

• Method

public class Solution {
    public String reverseWords(String s) {
        String[] tokens = s.trim().split(" +");
        Collections.reverse(Arrays.asList(tokens));
	    return String.join(" ", tokens);
    }
}

二刷

1. 想到通过split函数实现。
2. 有很多corner case需要考虑，个人觉得有一些corner case存在的价值不大。
3. 相比一刷通过正则和String的reverse，这次的方法快了很多。

   public class Solution {
    public String reverseWords(String s) {
        if(s == null || s.length() == 0) return s;
        String[] arr = s.split(" ");
        int len = arr.length;
        if(len == 0) return "";
        StringBuilder sb = new StringBuilder();
        sb.append(arr[len - 1]);
        for(int i = len - 2; i >= 0; i--)
            if(arr[i].length() > 0)
                sb.append(" " + arr[i]);
        return sb.toString();
    }
   }