[코테 풀이] Remove Outermost Parentheses

Q_1021) Remove Outermost Parentheses

출처 : https://leetcode.com/problems/remove-outermost-parentheses/

A valid parentheses string is either empty "", "(" + A + ")", or A + B, where A and B are valid parentheses strings, and + represents string concatenation.

For example, "", "()", "(())()", and "(()(()))" are all valid parentheses strings.

A valid parentheses string s is primitive if it is nonempty, and there does not exist a way to split it into s = A + B, with A and B nonempty valid parentheses strings.

Given a valid parentheses string s, consider its primitive decomposition: s = P1 + P2 + ... + Pk, where Pi are primitive valid parentheses strings.

Return s after removing the outermost parentheses of every primitive string in the primitive decomposition of s.

class Solution {
    public String removeOuterParentheses(String s) {
        Stack<Character> stack = new Stack<>();
        int count = -1;
        ArrayList<Integer> arrayList = new ArrayList<>();
        for (int i = 0; i < s.length(); i++) {
            count++;
            if (s.charAt(i) == '(') {
                stack.push(s.charAt(i));
            } else {
                stack.pop();
                if (stack.isEmpty()) arrayList.add(count);
            }
        }
        String answer = "";
        for (int a = 0; a < arrayList.size(); a++) {
            if (a == 0) answer += s.substring(1, arrayList.get(a));
            else answer += s.substring(arrayList.get(a - 1) + 2, arrayList.get(a));
        }
        return answer;
    }
}