[LeetCode][JAVA] 151. Reverse Words in a String

https://leetcode.com/problems/reverse-words-in-a-string/

At first, I used StringBuilder and ArrayList then added word in the list. Used one pointer.

class Solution {
    public String reverseWords(String s) {
        //pointer 만들기
        int pointer = 0;
        List<String> list = new ArrayList<>();

        //loop until the end of String
        while (pointer < s.length()) {
            StringBuilder word = new StringBuilder();

            //if char is not a blank, append to the word
            if (s.charAt(pointer) != ' ') {
                while (s.charAt(pointer) != ' ') {
                    word.append(s.charAt(pointer));
                    if (pointer == s.length() - 1) {
                        break;

                    }
                    pointer++;
                }
                list.add(word.toString());
            }

            pointer++;
        }

        Collections.reverse(list);

        StringBuilder sb = new StringBuilder();
       

        for (int i = 0; i < list.size(); i++) {
            sb.append(list.get(i));
            if (i != list.size() - 1) {
                sb.append(" ");
            }
        }

        return sb.toString();
    }
}

Then I saw a solution using two pointers. I solved again with two pointers.

class Solution {
    public String reverseWords(String s) {
       int n = s.length();

        //pointer 만들기
        int p1 = n - 1;

        //char[]
        char[] chars = s.toCharArray();

        //sb to return
        StringBuilder sb = new StringBuilder();

        //loop to the first of the s
        while (p1 >= 0) {
            if (chars[p1] == ' ') {
                p1--;
                continue;
            }
            //if it is not a space
            int p2 = p1 - 1;

            while (p2 >= 0 && chars[p2] != ' ') {
                p2--;
            }
            sb.append(s.substring(p2 + 1, p1 + 1));
            sb.append(' ');
            p1 = p2 - 1;
        }
        sb.deleteCharAt(sb.length() - 1);
        return sb.toString();
    }
}