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 = 9Output:true

**Example 2:**

Input:root = [5,3,6,2,4,null,7], k = 28Output:false

**Example 3:**

Input:root = [2,1,3], k = 4Output:true

**Example 4:**

Input:root = [2,1,3], k = 1Output:false

**Example 5:**

Input:root = [2,1,3], k = 3Output:true

**Constraints:**

- The number of nodes in the tree is in the range
`[1, 10`

.^{4}] `-10`

^{4}<= Node.val <= 10^{4}`root`

is guaranteed to be a**valid**binary search tree.`-10`

^{5}<= k <= 10^{5}