385. 迷你语法分析器

输入：s = "324",
输出：324
解释：你应该返回一个 NestedInteger 对象，其中只包含整数值 324。

输入：s = "[123,[456,[789]]]",
输出：[123,[456,[789]]]
解释：返回一个 NestedInteger 对象包含一个有两个元素的嵌套列表：
1. 一个 integer 包含值 123
2. 一个包含两个元素的嵌套列表：
    i.  一个 integer 包含值 456
    ii. 一个包含一个元素的嵌套列表
         a. 一个 integer 包含值 789

• 1 <= s.length <= 5 * 104

• s 由数字、方括号 "[]"、负号 '-' 、逗号 ','组成

• 用例保证 s 是可解析的 NestedInteger

• 输入中的所有值的范围是 [-106, 106]

法 1 栈模拟

• 遇到左括号，实例化一个 NestedInteger 放入栈中

• 遇到数字，那就先放到临时的num中。

• 遇到逗号，把当前维护的 num 实例化为 一个 NestedInteger 对象，且放到栈中

• 遇到右括号：
• 如果当前num 非空，需要把当前维护的 num 实例化为 一个 NestedInteger 对象，且放到栈中
• 且如果栈中多与两个 NestedInteger 对象，那么需要弹出栈顶的NestedInteger对象，且放入栈中倒数第二个NestedInteger 对象（即此时的栈顶）

# """
# This is the interface that allows for creating nested lists.
# You should not implement it, or speculate about its implementation
# """
#class NestedInteger:
#    def __init__(self, value=None):
#        """
#        If value is not specified, initializes an empty list.
#        Otherwise initializes a single integer equal to value.
#        """
#
#    def isInteger(self):
#        """
#        @return True if this NestedInteger holds a single integer, rather than a nested list.
#        :rtype bool
#        """
#
#    def add(self, elem):
#        """
#        Set this NestedInteger to hold a nested list and adds a nested integer elem to it.
#        :rtype void
#        """
#
#    def setInteger(self, value):
#        """
#        Set this NestedInteger to hold a single integer equal to value.
#        :rtype void
#        """
#
#    def getInteger(self):
#        """
#        @return the single integer that this NestedInteger holds, if it holds a single integer
#        Return None if this NestedInteger holds a nested list
#        :rtype int
#        """
#
#    def getList(self):
#        """
#        @return the nested list that this NestedInteger holds, if it holds a nested list
#        Return None if this NestedInteger holds a single integer
#        :rtype List[NestedInteger]
#        """
class Solution:
    def deserialize(self, s: str) -> NestedInteger:
        stack = []
        num = ""
        for char in s:
            # print(char, stack)
            if char == "[":
                stack.append(NestedInteger())
            elif char == ",":
                if num != "":
                    stack[-1].add(NestedInteger(int(num)))
                    num = ""
            elif char == "]":
                if num != "":
                    stack[-1].add(NestedInteger(int(num)))
                    num = ""
                if len(stack) > 1:
                    stack[-2].add(stack.pop())
            else:
                num += char

        return stack.pop() if stack else NestedInteger(int(num))