leetcode -- Flatten Binary Tree to Linked List
算法：
1. 对root的左子树做处理，让左子树的根节点作为，根节点的右子树，并让右子树作为左子树根节点的右子树的子树
2. 递归遍历右子树
public void flatten(TreeNode root) { if(root==null){ return; } if(root.left!=null){ TreeNode leftNode=root.left; TreeNode rightNode=root.right; root.left=null; root.right=leftNode; TreeNode tmp=leftNode;//root.left has been null while(tmp.right!=null){ tmp=tmp.right; } tmp.right=rightNode; } flatten(root.right); }