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Author: Partho Biswas

README.md

@@ -431,6 +431,7 @@ Check this [golden](https://tinyurl.com/ujopecz) post.
 |11| **[729. My Calendar I](https://tinyurl.com/r3ew2lb)** | [Python](https://tinyurl.com/wu6rdaw/729_My_Calendar_I.py), [Swift](https://tinyurl.com/wuja3c4/729_My_Calendar_I.swift)| [Art 1](https://tinyurl.com/tbd2z7u), [Art 2](https://tinyurl.com/t35fp3e) | Medium | Use self balancing BST for O(nlogn) solution. **Very important** |
 |12| **[449. Serialize and Deserialize BST](https://tinyurl.com/rx9rn3l)** | [Python](https://tinyurl.com/wu6rdaw/449_Serialize_and_Deserialize_BST.py), [Swift](https://tinyurl.com/wuja3c4/449_Serialize_and_Deserialize_BST.swift)| [Art 1](https://tinyurl.com/t6e2b97) | Medium | --- |
 |13| **[1008. Construct Binary Search Tree from Preorder Traversal](https://tinyurl.com/y6less2m)** | [Python](https://tinyurl.com/wu6rdaw/1008_Construct_Binary_Search_Tree_from_Preorder_Traversal.py), [Swift](https://tinyurl.com/wuja3c4/1008_Construct_Binary_Search_Tree_from_Preorder_Traversal.swift)| [Art 1](https://tinyurl.com/y9mondek), [Art 2](https://tinyurl.com/y8byt732), [Art 3](https://tinyurl.com/yaq7w2jt), [Art 4](https://tinyurl.com/ybwtzpzo) | Medium | --- |
+|14| **[653. Two Sum IV - Input is a BST](https://tinyurl.com/ydzdnawg)** | [Python](https://tinyurl.com/wu6rdaw/653_Two_Sum_IV_Input_is_a_BST.py), [Swift](https://tinyurl.com/wuja3c4/653_Two_Sum_IV_Input_is_a_BST.swift)| - | Easy | --- |
 
 </p>
 </details>

leetcode.com/python/653_Two_Sum_IV_Input_is_a_BST.py

@@ -0,0 +1,26 @@
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution(object):
+    def findTarget(self, root, k):
+        """
+        :type root: TreeNode
+        :type k: int
+        :rtype: bool
+        """
+        diffSet = set()
+        return self.findTargetHelper(root, k, diffSet)
+
+    def findTargetHelper(self, root, k, diffSet):
+        if not root:
+            return False
+        if root.val in diffSet:
+            return True
+        else:
+            diffSet.add((k - root.val))
+            left = self.findTargetHelper(root.left, k, diffSet)
+            right = self.findTargetHelper(root.right, k, diffSet)
+            return left or right