算法-算数表达式

def calculate(s: str) -> float:
    def helper(s_iter):
        stack = []
        num = 0.0
        sign = '+'

        while True:
            char = next(s_iter, None)
            if char is None or char in '+-*/)':
                if sign == '+':
                    stack.append(num)
                elif sign == '-':
                    stack.append(-num)
                elif sign == '*':
                    stack.append(stack.pop() * num)
                elif sign == '/':
                    stack.append(stack.pop() / num)

                if char is None or char == ')':
                    break

                sign = char
                num = 0.0
            elif char == '(':
                num = helper(s_iter)
            elif char.isdigit() or char == '.':
                # 处理数字和小数点
                num_str = char
                while True:
                    next_char = next(s_iter, None)
                    if next_char is None or not (next_char.isdigit() or next_char == '.'):
                        s_iter = itertools.chain([next_char], s_iter) if next_char is not None else s_iter
                        break
                    num_str += next_char
                num = float(num_str)

        return sum(stack)

    import itertools
    return helper(iter(s.replace(' ', '')))


# 测试示例
expression = "2+3.1 * 4-8.2/2"
print(f"输入: {expression}")
print(f"输出: {calculate(expression)}")  # 输出: 10.3

# 测试带括号的表达式
expression_with_parentheses = "2+3.1*(4-8.2)/2"
print(f"\n输入(带括号): {expression_with_parentheses}")
print(f"输出: {calculate(expression_with_parentheses)}")  # 输出: -2.521