Update FlattenBinaryTreeLinkedList.java

Submission Result: Invalid Error Code next not found

Submission Result: Compile Error

Line 18: cannot find symbol: class Node

Submission Result: Time Limit Exceeded

Last executed input:	{1,#,2} L 19 missing

Submission Result: Time Limit Exceeded

Last executed input:

Submission Result: Compile Error

Line 18: flatten(TreeNode) is already defined in Solution