Problem URL: Baseball game

We will use a stack to add the input and from there we will just follow the problem statement instruction. Finally we will return the sum of stack itself as result.

class Solution:
    def calPoints(self, operations: List[str]) -> int:
        stack = []
        for op in operations:
            if op == 'C':
                stack.pop()
            elif op == 'D':
                stack.append(stack[-1]*2)
            elif op == '+':
                stack.append(stack[-1]+stack[-2])
            else:
                stack.append(int(op))
        return sum(stack)

Time Complexity: O(n)
Space Complexity: O(n)