All problems

Solo Supervisors

Easy · tree dfs

A small company draws its org chart as a binary tree: every employee has at most two direct reports, a left one and a right one. The chart is given by its root, the head of the company.

A solo supervisor is an employee who has exactly one direct report: not none, and not two.

Return how many solo supervisors the chart contains. An empty chart contains none.

Examples

Example 1

Input: root = [8, 3, 5, 1, null, 2, 9]

Output: 1

Employee 3 has a single report (1). Employee 5 has two, and 8, 1, 2 and 9 have two or none.

Example 2

Input: root = [1, null, 2, null, 3]

Output: 2

Employee 1 supervises only 2, and employee 2 supervises only 3. Employee 3 has nobody.

Example 3

Input: root = []

Output: 0

Constraints