Find Whether a Complete Root Path Has a Target Sum
Company: Google
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Other
### Problem
Decide whether a binary tree contains a root-to-leaf path whose values add up to `targetSum`. Return a Boolean. The path must start at the root and end at a node with no children; stopping at an internal node is insufficient. An empty tree has no qualifying path.
```cpp
bool hasPathSum(TreeNode* root, int targetSum);
```
Keep the supplied `TreeNode` pointer interface. Brackets display level-order tree structure.
### Examples
```text
Input: root = [4,-2,7,3,null,-1,2], targetSum = 5
Output: true
```
The path 4→-2→3 sums to 5.
```text
Input: root = [4,-2], targetSum = 4
Output: false
```
The root has a child, so its value alone is not a root-to-leaf path.
### Constraints
- The tree contains between 0 and 5000 nodes.
- Every node value and `targetSum` are between -1000 and 1000, inclusive.
Overview: Test for a complete root-to-leaf value sum while handling empty trees, negative values and internal prefixes.