151. Reverse Words in a String

package LeetCode_151

/**
 * 151. Reverse Words in a String
 * https://leetcode.com/problems/reverse-words-in-a-string/
 *
 * 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"

Example 5:
Input: s = "Alice does not even like bob"
Output: "bob like even not does Alice"

Constraints:
1. 1 <= s.length <= 104
2. s contains English letters (upper-case and lower-case), digits, and spaces ' '.
3. There is at least one word in s.

Follow up:
Could you solve it in-place with O(1) extra space?
 * */
class Solution {
    fun reverseWords(s: String): String {
        //\\s+ can handle multi space, but in kotlin, need use toRegex() to fix escape character (ESC)
        val list = s.split("\\s+".toRegex())
        val n = list.size
        val result = StringBuilder()
        for(i in n-1 downTo 0){
            result.append(list[i]).append(" ")
        }
        return result.toString().trim()
    }
}