Leetcode: Inorder Successor in BST

Inorder Successor in BST



Similar Problems:


Given a binary search tree and a node in it, find the in-order successor of that node in the BST.

Note: If the given node has no in-order successor in the tree, return null.

Example 1:

Input: root = [2,1,3], p = 1

  2
 / \
1   3

Output: 2

Example 2:

Input: root = [5,3,6,2,4,null,null,1], p = 6

      5
     / \
    3   6
   / \
  2   4
 /   
1

Output: null

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.


  • Solution:

Intuitive Idea would have too many details.

## If p has right child, we can easily find the target in its sub-tree
## Otherwise: Use DFS to find all parents of p, from root down to p
##    If p is the left-subtree of q, q is the target
##    Otherwise keep looking up. If we get the root, return null
##
## Blog link: https://code.dennyzhang.com/inorder-successor-in-bst
## Basic Ideas:
## 
## Complexity:
# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def inorderSuccessor(self, root, p):
        """
        :type root: TreeNode
        :type p: TreeNode
        :rtype: TreeNode
        """
        if p is None or root is None: return None
        res = None
        while root:
            if root.val > p.val:
                # go to left
                res = root
                root = root.left
            else:
                # go to right
                root = root.right
        return res
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