题目：

题解：

class Solution:
    def deserialize(self, s: str) -> NestedInteger:
        index = 0

        def dfs() -> NestedInteger:
            nonlocal index
            if s[index] == '[':
                index += 1
                ni = NestedInteger()
                while s[index] != ']':
                    ni.add(dfs())
                    if s[index] == ',':
                        index += 1
                index += 1
                return ni
            else:
                negative = False
                if s[index] == '-':
                    negative = True
                    index += 1
                num = 0
                while index < len(s) and s[index].isdigit():
                    num *= 10
                    num += int(s[index])
                    index += 1
                if negative:
                    num = -num
                return NestedInteger(num)

        return dfs()