<p>Given a string s represents the serialization of a nested list, implement a parser to deserialize it and return <em>the deserialized</em> <code>NestedInteger</code>.</p>

<p>Each element is either an integer or a list whose elements may also be integers or other lists.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;324&quot;
<strong>Output:</strong> 324
<strong>Explanation:</strong> You should return a NestedInteger object which contains a single integer 324.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;[123,[456,[789]]]&quot;
<strong>Output:</strong> [123,[456,[789]]]
<strong>Explanation:</strong> Return a NestedInteger object containing a nested list with 2 elements:
1. An integer containing value 123.
2. A nested list containing two elements:
    i.  An integer containing value 456.
    ii. A nested list with one element:
         a. An integer containing value 789
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 5 * 10<sup>4</sup></code></li>
	<li><code>s</code> consists of digits, square brackets <code>&quot;[]&quot;</code>, negative sign <code>&#39;-&#39;</code>, and commas <code>&#39;,&#39;</code>.</li>
	<li><code>s</code> is the serialization of valid <code>NestedInteger</code>.</li>
	<li>All the values in the input are in the range <code>[-10<sup>6</sup>, 10<sup>6</sup>]</code>.</li>
</ul>

class Solution:
    def deserialize(self, s: str) -> NestedInteger:
        if s[0]!='[':
            return NestedInteger(int(s))
        num = None
        stack = []
        sign = '+'
        for i,char_ in enumerate(s):
            if char_ == '[':
                nested_ = NestedInteger()
                stack.append(nested_)
            elif char_ == '-':
                sign = '-'
            elif char_ == ']':
                if num!=None:
                    if sign=='-':
                        num = -num
                    stack[-1].add(NestedInteger(num))
                    num=None
                    sign='+'
                last_ = stack.pop()
                if stack:
                    stack[-1].add(last_)
                    last_= stack.pop()
                stack.append(last_)
            elif char_ == ',':
                if num!=None:
                    if sign=='-':
                        num = -num
                    stack[-1].add(NestedInteger(num))
                num = None
                sign='+'
            else:
                if num==None:
                    num = int(char_)
                else:
                    num = 10*num+int(char_)
        print(len(stack))
        return stack[0]

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