leetcode150 Evaluate Reverse Polish Notation

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are +, -, *, /. Each operand may be an integer or another expression.

Some examples:

[“2”, “1”, “+”, “3”, ““] -> ((2 + 1) 3) -> 9

[“4”, “13”, “5”, “/”, “+”] -> (4 + (13 / 5)) -> 6

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python

class Solution(object):
def isOp(self,s):
return s=="+" or s=="-" or s=="*" or s=="/"

def add(self,op1,op2):
return op1+op2

def sub(self,op1,op2):
return op1-op2

def mul(self,op1,op2):
return op1 * op2

def div(self,op1,op2):
if op1*op2<0:
return -((-op1)/op2)
return op1/op2

operator = {"+":add,"-":sub,"*":mul,"/":div}

def evalRPN(self,tokens):
nums=[]
for s in tokens:
if self.isOp(s):
op2 = nums.pop()
op1 = nums.pop()
re = self.operator.get(s)(self,op1,op2)
nums.append(re)
else:
nums.append(int(s))
return nums[0]