题目

https://leetcode-cn.com/problems/increasing-order-search-tree/

代码

class Solution {
    TreeNode pre;
    public TreeNode increasingBST(TreeNode root) {
        TreeNode tmp=new TreeNode(-1);
        pre=tmp;
        dfs(root);
        return tmp.right;
    }
    public void dfs(TreeNode root){
        if(root==null){
            return;
        }
        dfs(root.left);
        pre.right=root;
        root.left=null;
        pre=root;
        dfs(root.right);
    }
}

复杂度