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
解题思路：
试图通过排序后new TreeNode是无法通过的，这道题的意思是把现有的树进行剪枝操作。JAVA实现如下：
static public void flatten(TreeNode root) {
while(root!=null){
if(root.left!=null){
TreeNode pre = root.left;
while(pre.right!=null)
pre = pre.right;
pre.right = root.right;
root.right = root.left;
root.left = null;
}
root = root.right;
}
}
Java for LeetCode 114 Flatten Binary Tree to Linked List
原文：http://www.cnblogs.com/tonyluis/p/4524919.html