379. Zigzag Level Order
MediumBFS
Print the levels left to right, then right to left, alternating, one line per level.
Input format
Line 1: n (number of level-order entries) Line 2: the values in level order, -1 for a missing child
Output format
One line per level.
Example 1
Input
7 3 9 20 -1 -1 15 7
Output
3 20 9 15 7
Example 2
Input
7 1 2 3 4 5 6 7
Output
1 3 2 4 5 6 7
Constraints
1 ≤ nodes ≤ 10⁴
Read input from standard input and print the answer to standard output. Your code is judged against 3 test cases, most of them hidden.
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