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.
这道题是实现“迷你解释器”，题目难度为Medium。
字符串中括号存在层层嵌套的情况，所以需要借助栈来记录遍历路径上的每层NestedInteger。遇到'['时，表明即将进入新一层链表，此时构造新的NestedInteger并进栈；遇到']'时，表明该层链表结束，此时出栈并将该层链表通过add函数加入上层链表中。数字在遍历到']'或','时结束，此时将数字构造的NestedInteger通过add函数加入栈顶链表中，处理过程中需要记录数字的起始位置。另外，栈中最好存储指针，能够降低空间复杂度。具体代码：
/** * // 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[0] != '[') return NestedInteger(stoi(s)); stack<NestedInteger*> stk; NestedInteger* ret = NULL; int idx = 0; for(int i=0; i<s.size(); ++i) { if(s[i] == '[') { stk.push(new NestedInteger()); if(!ret) ret = stk.top(); idx = i + 1; } else if(s[i] == ']' || s[i] == ',') { if(idx != i) stk.top()->add(NestedInteger(stoi(s.substr(idx, i-idx)))); if(s[i] == ']') { NestedInteger* cur = stk.top(); stk.pop(); if(!stk.empty()) stk.top()->add(*cur); } idx = i + 1; } } return *ret; } };