Find Two Distinct BST Nodes Summing to a Target
Company: Google
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Other
### Problem
Return whether the binary search tree rooted at root has two different nodes whose values sum to k. The function receives TreeNode* with val,left,right; a node may not be reused as both summands.
```cpp
class Solution {
public:
bool findTarget(TreeNode* root, int k);
};
```
### Examples
**Example 1:**
```text
root = [8,3,11,1,6], k = 9
Output: true
Explanation: Nodes 3 and 6 sum to 9.
```
**Example 2:**
```text
root = [5], k = 10
Output: false
Explanation: The single node cannot be used twice.
```
### Constraints
- The input is a valid BST with 1..10000 nodes. Node values: -10000..10000. Target k: -100000..100000.
### Clarifying Questions
Enforce distinct nodes and check the complement before adding the current node to the seen set.
```hint Read the boundary condition
How can a complement lookup avoid matching a node with itself?
```
### Contract considerations
Enforce distinct nodes and check the complement before adding the current node to the seen set.
Overview: Find Two Distinct BST Nodes Summing to a Target. Return whether the binary search tree rooted at root has two different nodes whose values sum to k.