Leetcode 385 Solution

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * class NestedInteger {
 *   public:
 *     // Constructor initializes an empty nested list.
 *     NestedInteger();
 *
 *     // Constructor initializes a single integer.
 *     NestedInteger(int value);
 *
 *     // Return true if this NestedInteger holds a single integer, rather than a nested list.
 *     bool isInteger() const;
 *
 *     // Return the single integer that this NestedInteger holds, if it holds a single integer
 *     // The result is undefined if this NestedInteger holds a nested list
 *     int getInteger() const;
 *
 *     // Set this NestedInteger to hold a single integer.
 *     void setInteger(int value);
 *
 *     // Set this NestedInteger to hold a nested list and adds a nested integer to it.
 *     void add(const NestedInteger &ni);
 *
 *     // Return the nested list that this NestedInteger holds, if it holds a nested list
 *     // The result is undefined if this NestedInteger holds a single integer
 *     const vector<NestedInteger> &getList() const;
 * };
 */
class Solution {
public:
    NestedInteger deserialize(const string& s, int l, int r) {
        if ('0' <= s[l] && s[l] <= '9' || s[l] == '-')
            return NestedInteger(atoi(s.substr(l, r - l + 1).c_str()));
        else
        {
            NestedInteger res;

            int cnt = 0;
            int last_left = l + 1;
            for (int i = l + 1; i <= r; i++)
            {
                if ((s[i] == ',' && cnt == 0) || i == r)
                {
                    if (last_left <= i - 1)
                        res.add(deserialize(s, last_left, i - 1));
                    last_left = i + 1;
                }
                else if (s[i] == '[')
                    cnt++;
                else if (s[i] == ']')
                    cnt--;
            }

            return res;
        }
    }

    NestedInteger deserialize(string s) {
        return deserialize(s, 0, s.size() - 1);
    }
};