class Solution:
def calPoints(self, ops: List[str]) -> int:
stack = [] #得分栈
for op in ops:
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) #每轮得分求和