solution.cpp

/**
 * // 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;
 * };
 */

/**
 * 58 / 58 test cases passed.
 * Runtime: 12 ms
 * Memory Usage: 11.3 MB 
 */
class Solution {
public:
    NestedInteger deserialize(string s) {
        if (s.size() == 0) return NestedInteger();
        if (s[0] != '[') return NestedInteger(stoi(s));
        stack<NestedInteger> stk;
        int num = 0;
        int sign = 1;
        for (int i = 0; i < s.size(); ++ i) {
            char c = s[i];
            if (c == '-') sign = -1;
            else if (isdigit(c)) num = num * 10 + c - '0';
            else if (c == '[') stk.emplace(NestedInteger());
            else if (c == ',' || c == ']') {
                if (isdigit(s[i - 1])) 
                    stk.top().add(NestedInteger(sign * num));
                num = 0;
                sign = 1;
                if (c == ']' && stk.size() > 1) {
                    NestedInteger nested = stk.top(); stk.pop();
                    stk.top().add(nested);
                }
            }
        }
        return stk.top();
    }
};