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题目：（困难）

标签：字符串、栈

解法一：

class Solution:    def evaluate(self, expression: str) -> int:        value_stack = [[]]  # 表达式数据栈        param_stack = [{
   }]  # 表达式参数栈        for elem in expression.replace("(", "( ").replace(")", " )").split():            if elem == "(":                value_stack.append([])                param_stack.append(param_stack[-1].copy())            elif elem == ")":                values = value_stack.pop()                if values[0] == "add":                    value = values[1] + values[2]                elif values[0] == "mult":                    value = values[1] * values[2]                else:                    if isinstance(values[1], int):                        value = values[1]                    elif values[1].isdigit() or (values[1][0] == "-" and values[1][1:].isdigit()):                        value = int(values[1])                    else:                        value = param_stack[-1][values[1]]                value_stack[-1].append(value)                param_stack.pop()                if value_stack[-1][0] == "let" and len(value_stack[-1]) % 2 == 1:                    value = value_stack[-1].pop()                    param_stack[-1][value_stack[-1].pop()] = value            else:                if not value_stack[-1]:                    value_stack[-1].append(elem)                elif value_stack[-1][0] == "let":                    if len(value_stack[-1]) % 2 == 0:                        if elem.isdigit() or (elem[0] == "-" and elem[1:].isdigit()):                            param_stack[-1][value_stack[-1].pop()] = int(elem)                        else:                            param_stack[-1][value_stack[-1].pop()] = param_stack[-1][elem]                    else:                        value_stack[-1].append(elem)                else:                    if elem.isdigit() or (elem[0] == "-" and elem[1:].isdigit()):                        value_stack[-1].append(int(elem))                    else:                        value_stack[-1].append(param_stack[-1][elem])            # print(elem, "->", value_stack, param_stack)        return value_stack[0][0]

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