leetcode设计类题目

341. Flatten Nested List Iterator

Given a nested list of integers, implement an iterator to flatten it.

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

Example 1:
Given the list [[1,1],2,[1,1]],

By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,1,2,1,1].

Example 2:
Given the list [1,[4,[6]]],

By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,4,6].

这个题目需要反复复习，训练设计功底

/** * // This is the interface that allows for creating nested lists. * // You should not implement it, or speculate about its implementation * class NestedInteger { *   public: *     // 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; * *     // 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 NestedIterator {public:    NestedIterator(vector<NestedInteger> &nestedList) {//复制构造函数       int n=nestedList.size();        for(int i=n-1;i>=0;i--)        {            nodes.push(nestedList[i]);        }    }    int next() {        int res=nodes.top().getInteger();        nodes.pop();        return res;    }    bool hasNext() {        while(!nodes.empty())        {            NestedInteger cur=nodes.top();            if(cur.isInteger())                return true;            else            {                vector<NestedInteger>& ap=cur.getList();                nodes.pop();                for(int i=ap.size()-1;i>=0;i--)                {                    nodes.push(ap[i]);                }                            }        }        return false;    }private:    stack<NestedInteger> nodes;};/** * Your NestedIterator object will be instantiated and called as such: * NestedIterator i(nestedList); * while (i.hasNext()) cout << i.next(); */

385. 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.

/** * // 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) {        function<bool(char)> isNum=[](char c){return c=='-'||isdigit(c);};        stack<NestedInteger> res;        res.push(NestedInteger());        string::const_iterator it=s.begin();        for(auto it=s.begin();it!=s.end();)        {            char& c=*it;            if(isNum(c))            {                auto it2=find_if_not(it,s.end(),isNum);                int num=stoi(string(it,it2));                res.top().add(NestedInteger(num));                it=it2;            }            else            {                if(c=='[')                {                    res.push(NestedInteger());                }                else if(c==']')                {                    NestedInteger temp=res.top();                    res.pop();                    res.top().add(temp);                }                it++;            }                        }        return res.top().getList().front();    }};