BaseBall.java

// 682.Baseball Game
import java.util.Stack;

class Solution {
    public int calPoints(String[] operations) {
        Stack<Integer> stack = new Stack<>();

        for (String op : operations) {
            if (op.equals("C")) {
                stack.pop();
            } else if (op.equals("D")) {
                stack.push(stack.peek() * 2);
            } else if (op.equals("+")) {
                int top = stack.pop();
                int newTop = top + stack.peek();
                stack.push(top);
                stack.push(newTop);
            } else {
                stack.push(Integer.parseInt(op));
            }
        }

        int sum = 0;
        for (int score : stack) {
            sum += score;
        }

        return sum;
    }
}