150. Evaluate Reverse Polish Notation

solution.py

class Solution:
    VALID_OPERATIONS = set(["+", "-", "*", "/"])

    def evalRPN(self, tokens: List[str]) -> int:
        nums = []
        for token in tokens:
            if token not in Solution.VALID_OPERATIONS:
                nums.append(int(token))
                continue
            operand_two = nums.pop()
            operand_one = nums.pop()
            if token == "+":
                nums.append(operand_one + operand_two)
            if token == "-":
                nums.append(operand_one - operand_two)
            if token == "*":
                nums.append(operand_one * operand_two)
            if token == "/":
                nums.append(int(operand_one / operand_two))
        return nums[0]