def increasingBST(self, root, tail = None):
"""
:type root: TreeNode
:rtype: TreeNode
"""
if not root:
return tail
res = self.increasingBST(root.left, root)
root.left = None
root.right = self.increasingBST(root.right, tail)
return res
大概意思就是root.left.right = root, root.left = Null ？ 但是不理解怎么写， 为什么这么写
你先写下tree的 inorder traversal
看solution
class Solution {
TreeNode cur;
public TreeNode increasingBST(TreeNode root) {
TreeNode ans = new TreeNode(0);
cur = ans;
inorder(root);
return ans.right;
}
public void inorder(TreeNode node) {
if (node == null) return;
inorder(node.left);
node.left = null;
cur.right = node;
cur = node;
inorder(node.right);
}
}