《程序员面试金典》（第六版）习题：仅为记录一下以加强印象，不为商业用途，如有侵权请联系删除。以下源码和解释参考了书中源码以及解释。
     以下算法采用深度优先搜索解决。

class BinaryNode
{
private:int data;BinaryNode* left;BinaryNode* right;
public:BinaryNode(int value = 0, BinaryNode* pointer1 = nullptr, BinaryNode* pointer2 = nullptr){data = value;left = pointer1;right = pointer2;}BinaryNode* getLeft( ){return left;}BinaryNode* getRight(){return right;}
};void createLevelLinkedListHelper(BinaryNode* root, vector<forward_list<BinaryNode>*> & levelLinkedLists,int level)
{if (root == nullptr)return;forward_list<BinaryNode > *list = new forward_list<BinaryNode>();if (levelLinkedLists.size() == level){levelLinkedLists.push_back(list);}else{list = levelLinkedLists[level];}list->push_front(*root);createLevelLinkedListHelper(root->getLeft(), levelLinkedLists, level+1);createLevelLinkedListHelper(root->getRight(), levelLinkedLists, level+1);
}vector<forward_list<BinaryNode>*> createLevelLinkedList(BinaryNode *root)
{vector<forward_list<BinaryNode>*> levelLinkedLists = vector<forward_list<BinaryNode>*>();createLevelLinkedListHelper(root, levelLinkedLists, 0);return levelLinkedLists;
}

     以下算法采用广度优先搜索解决。

vector<forward_list<BinaryNode>*> createLevelLinkedListHelper(BinaryNode* root)
{vector<forward_list<BinaryNode>*> levelLinkedLists = vector<forward_list<BinaryNode>*>();if (root == nullptr)return;forward_list<BinaryNode > *current = new forward_list<BinaryNode>();current->push_front(*root);while (!current->empty()){levelLinkedLists.push_back(current);forward_list<BinaryNode >* parents = current;current = new forward_list<BinaryNode >();for (BinaryNode& parent : (*parents)){if (parent.getLeft() != nullptr){current->push_front(*parent.getLeft());}if (parent.getRight() != nullptr){current->push_front(*parent.getRight());}}}return levelLinkedLists;
}