题解 | 四则运算

def calculate(s: str) -> int:
    # 统一括号为小括号
    s = s.replace('{', '(').replace('}', ')')
    s = s.replace('[', '(').replace(']', ')')

    # 运算符优先级
    priority = {'+':1, '-':1, '*':2, '/':2}
    output = []       # 后缀表达式列表
    op_stack = []     # 运算符栈

    i = 0
    n = len(s)
    while i < n:
        c = s[i]

        # 1. 数字（多位数）
        if c.isdigit():
            num = 0
            while i < n and s[i].isdigit():
                num = num * 10 + int(s[i])
                i += 1
            output.append(num)
            continue

        # 2. 左括号
        if c == '(':
            op_stack.append(c)
            i += 1

        # 3. 右括号
        elif c == ')':
            while op_stack and op_stack[-1] != '(':
                output.append(op_stack.pop())
            op_stack.pop()  # 弹出左括号
            i += 1

        # 4. 运算符（+ - * /），处理一元负号
        elif c in '+-*/':
            # 判断是否为一元负号：开头、或前面是运算符/左括号
            if c == '-' and (i == 0 or s[i-1] in '+-*/('):
                output.append(0)  # 补一个0，把一元负号变成 0 - x
            # 弹出栈中优先级 >= 当前运算符的运算符
            while op_stack and op_stack[-1] != '(' and priority[op_stack[-1]] >= priority[c]:
                output.append(op_stack.pop())
            op_stack.append(c)
            i += 1

        else:
            i += 1

    # 弹出剩余运算符
    while op_stack:
        output.append(op_stack.pop())

    # 计算后缀表达式
    calc_stack = []
    for token in output:
        if isinstance(token, int):
            calc_stack.append(token)
        else:
            b = calc_stack.pop()
            a = calc_stack.pop()
            if token == '+':
                res = a + b
            elif token == '-':
                res = a - b
            elif token == '*':
                res = a * b
            elif token == '/':
                # 题目保证整除，且结果为整数，向0取整
                res = int(a / b)
            calc_stack.append(res)

    return calc_stack[0]


if __name__ == "__main__":
    s = input().strip()
    print(calculate(s))

# 评论区看到的不讲武德的解法
# while True:
#     try:
#         exp = input()
#         exp = exp.replace("[", "(").replace("]", ")")
#         exp = exp.replace("{", "(").replace("}", ")")
#         print(int(eval(exp)))
#     except:
#         break