題目描述連結：https://leetcode-cn.com/problems/list-of-depth-lcci/

解題思路：採用廣度優先搜尋，進行層次遍歷，每層訪問時將每層的節點新增到相應層對應的連結串列當中，訪問完一層將該層的連結串列放到答案陣列中。

具體LeetCode參考程式碼如下：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 
 
*/
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    vector<ListNode*> listOfDepth(TreeNode* tree) {
        queue<TreeNode*>q;
        q.push(tree);
        vector
 
<ListNode*>res;
        TreeNode *p;
        int len;
        while(!q.empty()){
            len=q.size();
            ListNode *root=new ListNode(0);
            ListNode *temp;
            temp=root;
            for(int i=0;i<len;++i){
               p=q.front();
               q.pop();
               
 
if(p->left){
                   q.push(p->left);
               }
               if(p->right){
                   q.push(p->right);
               }
               
               ListNode *temp2=new ListNode(p->val);
               
               temp->next=temp2;
              
               temp=temp2;
               
            }
           
            res.push_back(root->next);
        }
        return res;
    }
};