897. Increasing Order Search Tree

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def increasingBST(self, root: TreeNode) -> TreeNode:
        if root is None:
            return None
        left = self.increasingBST(root.left)
        right = self.increasingBST(root.right)
        if left is None:
            root.right = right
            return root
        res = left
        while left and left.right:
            left = left.right
        left.right = root
        root.right = right
        root.left = None
        return res

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public TreeNode increasingBST(TreeNode root) {
        if (root == null) return null;
        TreeNode left = increasingBST(root.left);
        TreeNode right = increasingBST(root.right);
        if (left == null) {
            root.right = right;
            return root;
        }
        TreeNode res = left;
        while (left != null && left.right != null) left = left.right;
        left.right = root;
        root.right = right;
        root.left = null;
        return res;
    }
}