[LeetCode] (medium) 385. Mini Parser

https://leetcode.com/problems/mini-parser/

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:

Given s = "324",

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

 

Example 2:

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.

---

都叫Nested了，肯定是递归做

如果用栈迭代实现速度反而慢（当然不排除是stoi的关系）

 

迭代：

/**
 * // 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(string s) {
        // s[s.size()-1] = ',';
        stack<NestedInteger> S;
        S.emplace();
        int cur = 0;
        while(cur < s.size()){
            if(s[cur] == '['){
                S.emplace();
                ++cur;
            }else if(s[cur] == ']'){
                NestedInteger tem = S.top();    S.pop();
                // if(tem.getList().size() == 1){
                //     tem = tem.getList()[0];
                // }
                S.top().add(tem);
                ++cur;
            }else if(s[cur] == ','){
                ++cur;
            }else{
                int cur_num = 0;
                
                //get num
                bool positive = true;
                
                if(s[cur] == '-'){
                    positive = false;
                    ++cur;
                }
                
                while(s[cur] >= '0' && s[cur] <= '9'){
                    cur_num = cur_num*10-(s[cur]-'0');
                    ++cur;
                }
                
                if(positive) cur_num = -cur_num;
                
                
                S.top().add(NestedInteger(cur_num));
            }
        }
        
        return S.top().getList()[0];
    }
};

 

递归：

class Solution {
public:
    NestedInteger deserialize(string s) {
        // cout << "entered: " << s << endl;
        if(s.size() == 0) return NestedInteger();
        if(s[0] != '[') return NestedInteger(stoi(s));
        if(s.size() == 2) return NestedInteger();
        
        int st = 1, cnt = 0;
        
        NestedInteger result;
        
        for(int i = 1; i < s.size(); ++i){
            if(cnt == 0 && (s[i] == ',' || i == s.size()-1)){
                // cout << s.substr(st, i-st) << endl;
                result.add(deserialize(s.substr(st, i-st)));
                st = i+1;
            }else if(s[i] == '['){
                ++cnt;
            }else if(s[i] == ']'){
                --cnt;
            }
            
        }
        
        return result;
    }
};