逆波蘭就是后序
輸入：tokens = ["10","6","9","3","+","-11","*","/","*","17","+","5","+"]
輸出：22
def?evalRPN(self,?tokens):
????????stack?=?[]
????????for?token?in?tokens:
????????????if?token?==?'+':
????????????????stack.append(int(stack.pop()?+?stack.pop()))
????????????elif?token?==?'-':
????????????????stack.append(int(-1?*?stack.pop()?+?stack.pop()))
????????????elif?token?==?'*':
????????????????stack.append(int(stack.pop()?*?stack.pop()))
????????????elif?token?==?'/':
????????????????denometor?=?stack.pop()
????????????????stack.append(int(stack.pop()?/?denometor))
????????????else:
????????????????stack.append(int(token))
????????return?stack.pop()
