Mini Parser

Desicription

Given a nested list of integers represented as a string, implement a parser to deserialize it.

Each element is either an integer, or a list – whose elements may also be integers or other lists.

Note: You may assume that the string is well-formed:

  • String is non-empty.
  • String does not contain white spaces.
  • String contains only digits 0-9, [, - ,, ].

Example 1:

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Given s = "324",

You should return a NestedInteger object which contains a single integer 324.

Example 2:

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Given s = "[123,[456,[789]]]",

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.

Solution

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/**
 * // 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 std::string& s) {
        auto stack = std::stack<NestedInteger>{};
        int number = 0;
        bool flag = true;
        bool haveNumber = false;
        for(const auto& c : s) {
            switch(c) {
                case '[':
                    stack.push(NestedInteger{});
                    break;
                case ']':
                    if(flag == false) {
                        number = -number;
                    }
                    if(haveNumber == true) {
                        stack.top().add(NestedInteger{number});
                        number = 0;
                        flag = true;
                        haveNumber = false;
                    }

                    if(stack.size() == 1) {
                        return stack.top();
                    } else {
                        auto tmpNestedInteger = stack.top();
                        stack.pop();
                        stack.top().add(tmpNestedInteger);
                    }
                    break;
                case ',':
                    if(flag == false) {
                        number = -number;
                    }
                    if(haveNumber == true) {
                        stack.top().add(NestedInteger{number});
                        number = 0;
                        flag = true;
                        haveNumber = false;
                    }
                    break;
                case '-':
                    flag = false;
                    break;
                default:
                    number = number * 10 + c - '0';
                    haveNumber = true;
                    break;
            }
        }
        if(number != 0) {
            if(flag == false) {
                number = -number;
            }
            if(haveNumber == true) {
                stack.push(NestedInteger{number});
            }
        }
        return stack.empty() ? NestedInteger{0} : stack.top();
    }
};