150. 逆波兰表达式求值 - 力扣（LeetCode）
class Solution:def evalRPN(self, tokens: List[str]) -> int:stack=[]for item in tokens:if item not in ( '+','-','*' , '/' ):stack.append(item)else:pre=int(stack.pop())pre_before=int(stack.pop())sign =itemif sign =='/':result=int(pre_before/pre)elif sign =='+':result=pre_before+preelif sign =='-':result=pre_before-preelif sign =='*':result=pre_before*prestack.append(result)return int(stack.pop())
