Create 653_TwoSum_IV-Input_is_a_BST.md

Author: koji

653_TwoSum_IV-Input_is_a_BST.md

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+Given the root of a Binary Search Tree and a target number k, return true if there exist two elements in the BST such that their sum is equal to the given target.
+
+ 
+
+Example 1:
+Input: root = [5,3,6,2,4,null,7], k = 9
+Output: true
+
+Example 2:
+Input: root = [5,3,6,2,4,null,7], k = 28
+Output: false
+
+Example 3:
+Input: root = [2,1,3], k = 4
+Output: true
+
+Example 4:
+Input: root = [2,1,3], k = 1
+Output: false
+
+Example 5:
+Input: root = [2,1,3], k = 3
+Output: true
+ 
+
+Constraints:
+
+The number of nodes in the tree is in the range [1, 104].
+-104 <= Node.val <= 104
+root is guaranteed to be a valid binary search tree.
+-105 <= k <= 105
+
+
+```python
+def findTarget(self, root: TreeNode, k: int) -> bool:
+ if root == None: return False
+ visited = set()
+ def traverse(cur):
+ if cur == None: return False
+ if k-cur.val in visited: return True
+ visited.add(cur.val)
+ return traverse(cur.left) or traverse(cur.right)
+ return traverse(root)
+```