Level order print problem solutions

Submitted solutions

Luís Armando Bianchin in Python (gist) (neat python list comprehensions!—an expected followup question would be: "can you do this without accessing the children twice per level?")
Bernie Margolis in Java (gist) (neat interfaces! uses lists on different levels of the call stack with recursion to track level advance)
Travis Jones in C (gist) and explanation with pictures (wild technique!)
Ankit Goyal in Ruby (gist) (uses counter to track when row is over)
Michael Penkov in Python (gist) (stores node level paired with children) "The solution is pretty ordinary: it's an iterative breadth-first search. I keep track of the level of each node I'm traversing. This is quite wasteful: I didn't think of using sentinels as in the sample solution. Given that BFS is generally memory-limited, sentinels are definitely the way to go."
Asim Ihsan in Java (imgur of initial thinking, gist (collects nodes until seeing sentinel, then prints and adds new level-indicating sentinel)
Denis Karpenko in Ruby (gist) (maps levels to values, then frees up memory early)
Omid Houshyar in Perl (gist)

Last week's question was to print a binary tree of integers in level order.

Level-order printing means printing each row of the tree from left to right, from root row to the deepest row. After each row, print a newline.

For example:

Bonus 1: Make one version that supports binary trees, and another that can handle any K-ary tree

Bonus 2: Submit your solution to Blake Embrey's problem repository