341. Flatten Nested List Iterator

方法1:NestedInteger实际上是一个树结构，递归实现。

class NestedIterator {
public:
    NestedIterator(vector<NestedInteger> &nestedList) {
        int len=nestedList.size();
        int it=0;
        
        while(it<len)
        {
            NestedInteger vec=nestedList[it];
            if(vec.isInteger())
            {
                ans.push_back(vec.getInteger());
            }
            else
            {
                vector<NestedInteger> vt=vec.getList();
                NestedIterator obj(vt);
                while(obj.hasNext())
                {
                    ans.push_back(obj.next());
                }
            }
            it++;
        } 
        pos=0;
        Max=ans.size();
    }
    
    int next() {
        return ans[pos++];
    }
    
    bool hasNext() {
        if(pos<Max)
            return true;
        return false;
    }
private:
    int Max;
    int pos;
    vector<int> ans;
};

方法2:

非递归方式

/**
 * // 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) {
        begins.push(nestedList.begin());
        ends.push(nestedList.end());
    }
    
    int next() { 
        return (begins.top()++)->getInteger();
    }
    
    bool hasNext() {
        while(begins.size())
        {
            if(begins.top()==ends.top())
            {
                begins.pop();
                ends.pop();
                continue;
            }
            auto tmp=begins.top();
            if(tmp->isInteger()) 
            {
                cout<<tmp->getInteger()<<endl;
                return true;
            }
            
            begins.top()++;
            vector<NestedInteger> &vec=tmp->getList();
            begins.push(vec.begin());
            ends.push(vec.end());
        }
        return false;
    }
private:
    stack<vector<NestedInteger>::iterator> begins,ends;
};


/**
 * Your NestedIterator object will be instantiated and called as such:
 * NestedIterator i(nestedList);
 * while (i.hasNext()) cout << i.next();
 */