TreeBFSQueue
Print the nodes of a binary tree level by level, from left to right, one level per line. Build the tree from the level-order input yourself, then solve the problem.
Input
A single line giving the tree in level order, with the word null for a missing child (for example 3 9 20 null null 15 7).
Output
One line per level, with that level's values separated by spaces.
Constraints
1 <= number of nodes <= 2000
Example 1
Input
3 9 20 null null 15 7
Output
3 9 20 15 7
Levels: 3 / 9 20 / 15 7.