Lintcode 424. Evaluate Reverse Polish Notation (Medium) (Python)

Evaluate Reverse Polish Notation

Description:

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

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

Example
[“2”, “1”, “+”, “3”, ““] -> ((2 + 1) 3) -> 9
[“4”, “13”, “5”, “/”, “+”] -> (4 + (13 / 5)) -> 6

Code:

class Solution:
    """
    @param tokens: The Reverse Polish Notation
    @return: the value
    """
    def evalRPN(self, tokens):
        # write your code here
        stack = []
        for i in tokens:
            if i.isnumeric() or i[1:].isnumeric():
                stack.append(int(i))
            else:
                par2 = stack.pop()
                par1 = stack.pop()
                if i=='+':
                    stack.append(par1+par2)
                if i=='-':
                    stack.append(par1-par2)
                if i=='*':
                    stack.append(par1*par2)
                if i=='/':
                    stack.append(int(par1/par2))
        return int(stack.pop())