QUESTION 4
We talked about using data structure queue to implement level order traversal for binary trees. For example, level order traversal of following binary
tree would output [10, 5, 20, 3, 8, 12, 30]. Now please design and implement a function that takes in tree's root, delete the whole binary tree, and
set the root to nullptr. You may use queue for this function, and its time complexity should be O(n).