Your task is to write a program that reads a non empty binary tree of natural numbers, and prints its level order traversal (that is, from top to bottom and from left to right), with a line for each level.
(To see an instance of the tree corresponding to the input-output instance, consult the pdf or ps version of this wording.)
Input
The input consists of the description of non empty a binary tree of natural numbers as it is explained at the exercise : “” of the subject collection.
Output
Your program must print as many lines as levels, with the level order traversal of the tree. Follow the format of the instances.
Input
10 3 0 7 -1 4 -1 -1 2 -1 -1 5 4 -1 -1 7 6 -1 1 -1 -1 -1
Output
level 1: 3 level 2: 0 5 level 3: 7 2 4 7 level 4: 4 6 level 5: 1
Input
1 7 -1 -1
Output
level 1: 7
Input
4 9 -1 8 7 -1 6 -1 -1 -1
Output
level 1: 9 level 2: 8 level 3: 7 level 4: 6