[LeetCode&Python] Problem 897. Increasing Order Search Tree

Given a tree, rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree, and every node has no left child and only 1 right child.

Example 1:
Input: [5,3,6,2,4,null,8,1,null,null,null,7,9]

       5
      / \
    3    6
   / \    \
  2   4    8
 /        / \ 
1        7   9

Output: [1,null,2,null,3,null,4,null,5,null,6,null,7,null,8,null,9]

 1
  \
   2
    \
     3
      \
       4
        \
         5
          \
           6
            \
             7
              \
               8
                \
                 9  

Note:

1. The number of nodes in the given tree will be between 1 and 100.
2. Each node will have a unique integer value from 0 to 1000.

 

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def increasingBST(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        head=TreeNode(0)
        head.right=root
        p=head
        q=root
        
        while q:
            if q.left:
                r=q.left
                while r.right: r=r.right
                r.right=q
                p.right=q.left
                q.left=None
                q=p.right
            else:
                p=q
                q=q.right
                
        return head.right