Solution of Recovering Binary Search Tree

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|