내 풀이 - Stack 사용 , 백준에서 비슷한 문제를 풀어봄

import java.util.Stack;

class Solution {
    final int[] hamberger = {1, 2, 3, 1};

    public int solution(int[] ingredient) {
        int answer = 0;

        Stack<Integer> stack = new Stack<>();

        for (int val : ingredient) {
            stack.push(val);

            if (stack.size() >= 4 && stack.peek() == 1) {
                int changeIdx = stack.size() - 4;
                boolean makeFlag = true;

                for (int tmpIdx = 0; tmpIdx < 4; tmpIdx++) {
                    if (stack.get(changeIdx + tmpIdx) != hamberger[tmpIdx]) {
                        makeFlag = false;
                        break;
                    }
                }

                if (makeFlag) {
                    for (int j = 0; j < 4; j++) {
                        stack.pop();
                    }

                    answer++;
                }
            }
        }

        return answer;
    }
}

다른 사람 풀이 - 배열 사용 - 속도 매움 빠름

class Solution {
    public int solution(int[] ingredient) {
        int[] stack = new int[ingredient.length];
        int sp = 0;
        int answer = 0;
        for (int i : ingredient) {
            stack[sp++] = i;
            if (sp >= 4 && stack[sp - 1] == 1
                && stack[sp - 2] == 3
                && stack[sp - 3] == 2
                && stack[sp - 4] == 1) {
                sp -= 4;
                answer++;
            }
        }
        return answer;
    }
}