LeetCode 150 - Evaluate Reverse Polish Notation - 2023.10.29 solution

class Solution:
    def evalRPN(self, tokens: List[str]) -> int:
        """ Approach: Step through the input while adding the numbers to a stack,
        and if you come to a point where the
        current entry is an operator, pop the last two entries and perform the
        operation, and then add the result back onto the stack.
        """
        stack = []

        for t in tokens:
            if t not in {'+', '-', '*', '/'}:
                stack.append(int(t))
            else:
                second_operand = stack.pop()
                first_operand = stack.pop()
                if t == '+':
                    stack.append(first_operand + second_operand)
                elif t == '-':
                    stack.append(first_operand - second_operand)
                elif t == '*':
                    stack.append(first_operand * second_operand)
                elif t == '/':
                    stack.append(int(first_operand / second_operand))

        return stack.pop()