870. Count Half Nodes in Binary Tree

Given the root of a binary tree, return the number of half nodes — nodes that have exactly one child (either left or right, but not both). The tree is given as a level-order array with null for missing children.

Input: A level-order array of the tree.

Output: Integer — the number of half nodes.

Examples

Input: [1,2,3,4,null,null,7]
Output: 2
Explanation: Nodes 2 and 3 each have exactly one child.

Input: [1,2,3]
Output: 0
Explanation: No half nodes.

Input: [1,2]
Output: 1
Explanation: Root has one child.

Constraints

• 0<=nodes<=10^4
• -1000<=value<=1000

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