Solution of Recovering Binary Search Tree

Author: Garvit244

1-100q/99.py

@@ -0,0 +1,53 @@
+'''
+Two elements of a binary search tree (BST) are swapped by mistake.
+
+Recover the tree without changing its structure.
+
+Example 1:
+
+Input: [1,3,null,null,2]
+
+ 1
+ /
+ 3
+ \
+ 2
+
+Output: [3,1,null,null,2]
+
+ 3
+ /
+ 1
+ \
+ 2
+'''
+# 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 recoverTree(self, root):
+ """
+ :type root: TreeNode
+ :rtype: void Do not return anything, modify root in-place instead.
+ """
+
+ first, second, prev = None, None, None
+ def inorder(root):
+ if root:
+ inorder(root.left)
+ if prev is not None and root.val < prev.val:
+ if first is None:
+ first = root
+ else:
+ second = root
+ prev = root
+ inorder(root.right)
+
+
+ inorder(root)
+ if first and second:
+ first.val, second.val = second.val, first.val

README.md

@@ -96,6 +96,7 @@ Python solution of problems from [LeetCode](https://leetcode.com/).
 ##### [Problems 1-100](./1-100q/)
 | # | Title | Solution | Difficulty |
 |---| ----- | -------- | ---------- |
+|99|[Recover Binary Search Tree](https://leetcode.com/problems/recover-binary-search-tree)|[Python](./1-100q/99.py)|Hard|
 |98|[Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/)| [Python](./1-100q/98.py)|Medium|
 |97|[Interleaving String](https://leetcode.com/problems/interleaving-string/)| [Python](./1-100q/97.py)|Hard|
 |95|[Unique Binary Search Trees II](https://leetcode.com/problems/unique-binary-search-trees-ii/)| [Python](./1-100q/95.py)|Medium|