[682. Baseball Game] #leetcode

682_0923.java

class Solution {
    public int calPoints(String[] ops) {
        int sum = 0;
        if (ops.length == 0 || ops == null) return sum;
        
        Deque<Integer> stack = new LinkedList<Integer>();
        for (int i = 0 ; i < ops.length ; i++) {
            if (ops[i].matches("-?\\d+(\\.\\d+)?")) {
                int val = Integer.valueOf(ops[i]);
                stack.addLast(val);
                sum += val;
            } else if (ops[i].equals("+")) {
                int lastOne = 0, lastTwo = 0;
                
                if (stack.size() != 0) {
                    lastOne = stack.removeLast();    
                    
                    if (stack.size() != 0) {
                        lastTwo = stack.peekLast();
                    }
                    
                    stack.addLast(lastOne);
                }
                
                stack.addLast(lastOne + lastTwo);
                sum += lastOne + lastTwo;
            } else if (ops[i].equals("D")) {
                if (stack.size() != 0) {
                    sum += stack.peekLast() * 2;
                    stack.addLast(stack.peekLast() * 2);
                }
            } else {
                if (stack.size() != 0) {
                    sum -= stack.removeLast();
                }
            }
        }
        
        return sum;
    }
}