Given the following definition of a 2-3-4 Tree node (using Java):

public class Node234 { public int keys[3]; public Node234 children[4]; };

Design an algorithm (pseudocode, C++, Java, or Python) to print the numbers of the tree in order. Assume blank key values are represented with as -1 and should not be printed. Child nodes that do not exist will be null. The algorithm should use the following function signature:

public printInOrder(Node234 current)

The function will be called starting at the root as in:

printInOrder(root);