Interleave Two Queues

Write a function queue<int> interleave(queue<int> a, queue<int> b) that returns a new queue built by alternating elements: first the front of a, then the front of b, then the next element of a, then the next of b, and so on. When one queue runs out, append all remaining elements of the other.

The tests drain the returned queue and print the values separated by spaces. For a = {1, 2, 3} and b = {10, 20} the output is exactly what is shown in Expected Output.

For a = {1, 2} and b = {10, 20, 30, 40} the output is:
1 10 2 20 30 40

Do NOT write a main function.