Flatten Binary Tree to Linked List Given a binary tree, flatten it to a linked list in-place. For example,Given 1 / \ 2 5 / \ \ 3 4 6 The flattened tree should look like: 1 \ 2 \ 3 \ 4 \ 5 \ 6 SOLUTION 1:使用递归解决,根据left是否为空,先连接left tree, 然后再连接右子树.使用一个t…