[Leetcode] 385. Mini Parser 解题报告

题目：

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.

思路：

一道字符串解析的题目，根据NestedInteger的定义，我们一定是需要用到DFS的。具体思路是：

1）如果要解析的字符串的首字母不是'['，那么一定是一个整数，直接返回对应的整数就可以；

2）否则首先根据逗号分割出list中的每个元素，然后递归调用函数，将返回结果赋给parent即可。

不多解释，直接上代码。

代码：

/** * // 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) {        if (s.length() == 0) {            return NestedInteger();        }        return deserialize(s, 0, s.length() - 1);    }private:    NestedInteger deserialize(string &s, int left, int right) {        if(s[left] == '[') {      // should be a list            NestedInteger parent;            if(right == left + 1) {                return parent;            }            int start = left + 1;            int pairs = 0;            NestedInteger ni;            for(int end = left + 1; end <= right - 1; ++end) {                if(s[end] == '[')       pairs++;                else if(s[end] == ']')  pairs--;                else if(s[end] == ',' && pairs == 0) {                    ni = deserialize(s, start, end - 1);                    parent.add(ni);                    start = end + 1;                }            }            ni = deserialize(s, start, right - 1);            parent.add(ni);            return parent;        }        else {                   // should be a integer value            int value = stoi(s.substr(left, right - left + 1));            return NestedInteger(value);        }    }};