用于评估算术表达式的程序

Question

这是一个我还没有解决的有趣问题。

给出Reverse Polish Notation中的算术表达式，编写一个程序对其求值。

该表达式作为数字和操作数的列表给出。例如，[5, 3, '+']应该返回5 + 3 = 8。

例如，

[15, 7, 1, 1, '+', '-', '/', 3, '*', 2, 1, 1, '+', '+', '-']

应该返回5，因为它等效于((15 / (7 - (1 + 1))) * 3) - (2 + (1 + 1)) = 5。

Answer 1

ops = {
    "+": (lambda a, b: a + b),
    "-": (lambda a, b: a - b),
    "*": (lambda a, b: a * b),
    "/": (lambda a, b: a / b)
}


def pol(tokens):
    stack = []

    for token in tokens:
        # Check if the current element is an operator
        if token in ops:
            # Take the last two elements from the list
            arg2 = stack.pop()
            arg1 = stack.pop()
            # Execute an operation based on the current operator
            result = ops[token](arg1, arg2)
            # Append the result to the list in order to keep working with it
            stack.append(result)
        else:
            # If it is a number, just append in to the list
            stack.append(int(token))

    return stack.pop()


print(pol([15, 7, 1, 1, '+', '-', '/', 3, '*', 2, 1, 1, '+', '+', '-']))