计算算术表达式的程序

Question

这是一个有趣的问题，我还没有设法解决。

给定 Reverse Polish Notation 中的一个算术表达式，编写一个程序来计算它。

表达式以数字和操作数的列表形式给出。例如 [5, 3, '+'] 应该 return 5 + 3 = 8.

例如，

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

应该 return 5 因为它等同于 ((15 / (7 - (1 + 1))) * 3) - (2 + (1 + 1)) = 5.

Answer 1

这段代码可以完成工作：

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, '+', '+', '-']))

Answer 2

尝试用字符串方法解决。


import re

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

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

while len(d) > 1:
    s_d = ' '.join(map(str, d))
    l_d = re.findall(r'\d+ \d+ \W', s_d)
    # print(l_d)
    for l1 in l_d:
        l = l1.split(' ')
        a = int(ops[l[-1]](int(l[0]),int(l[1])))
        s_d = s_d.replace(l1, str(int(a)))

    d = s_d.split()

    print(d)
print('----------------------')
print(d[0])

计算算术表达式的程序

A program to evaluate arithmetic expression

python

algorithm

arithmetic-expressions