Baseball Game

1import java.util.Stack;
2
3class Solution {
4    public int calPoints(String[] operations) {
5        Stack<String> stack = new Stack<String>();
6
7        for (int i = 0; i < operations.length; i++) {
8            if (operations[i].equals("D")) {
9                int peeked = Integer.parseInt(stack.peek());
10                stack.push(Integer.toString(peeked * 2));
11            }
12            else if (operations[i].equals("C")) {
13                stack.pop();
14            }
15            else if (operations[i].equals("+")) {
16                String popped = stack.pop();
17                int operand1 = Integer.parseInt(popped);
18                int operand2 = Integer.parseInt(stack.peek());
19                stack.push(popped);
20                stack.push(Integer.toString(operand1 + operand2));
21            }
22            else {
23                // an integer
24                stack.push(operations[i]);
25            }
26        }
27
28        int sum = 0;
29        while (!stack.isEmpty()) {
30            sum += Integer.parseInt(stack.pop());
31        }
32
33        return sum;
34    }
35}