<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 {
public:
    NestedInteger deserialize(string s) {
        int N = s.size();
        if(s.empty() || s[0] != '[') {
            return NestedInteger(stoi(s));
        }

        s = s.substr(1, N - 2);
        N = s.size();

        // Find all the comma's indices.
        vector<int> commas;
        int open = 0;
        for(int i=0; i<N; i++) {
            if(s[i] == '[') open++;
            else if(s[i] == ']') open--;

            if(open == 0 && s[i] == ',') {
                commas.push_back(i);
            }
        }

        // Handle each element
        vector<string> elements;
        
        int prev = 0;
        for(int idx : commas) {
            elements.push_back(s.substr(prev, idx-prev));
            prev = idx+1;
        }
        if(prev < N) {
            elements.push_back(s.substr(prev, N-prev));
        }
        
        NestedInteger ret;
        for(string e : elements) {
            ret.add(deserialize(e));
        }

        return ret;
    }
};
21100