Solution.py

class Solution:
    def evaluate(self, expression: str) -> int:
        def parseVar():
            nonlocal i
            j = i
            while i < n and expression[i] not in " )":
                i += 1
            return expression[j:i]

        def parseInt():
            nonlocal i
            sign, v = 1, 0
            if expression[i] == "-":
                sign = -1
                i += 1
            while i < n and expression[i].isdigit():
                v = v * 10 + int(expression[i])
                i += 1
            return sign * v

        def eval():
            nonlocal i
            if expression[i] != "(":
                return scope[parseVar()][-1] if expression[i].islower() else parseInt()
            i += 1
            if expression[i] == "l":
                i += 4
                vars = []
                while 1:
                    var = parseVar()
                    if expression[i] == ")":
                        ans = scope[var][-1]
                        break
                    vars.append(var)
                    i += 1
                    scope[var].append(eval())
                    i += 1
                    if not expression[i].islower():
                        ans = eval()
                        break
                for v in vars:
                    scope[v].pop()
            else:
                add = expression[i] == "a"
                i += 4 if add else 5
                a = eval()
                i += 1
                b = eval()
                ans = a + b if add else a * b
            i += 1
            return ans

        i, n = 0, len(expression)
        scope = defaultdict(list)
        return eval()