Given a binary tree, design an algorithm which creates a linked list of all the nodes at each depth (e.g., if you have a tree with depth D, you'll have D linked lists). Return a array containing all the linked lists.
Example:
Input: [1,2,3,4,5,null,7,8]
1
/ \
2 3
/ \ \
4 5 7
/
8
Output: [[1],[2,3],[4,5,7],[8]]