The tree is given by the list of arcs. The first array is the beginning of the arc, the second array is the end of the arc.

`A(2, 2, 3, 3, 5, 5, 6, 9, 1) B(3, 5, 6, 9, 4, 1, 10, 15, 22)`

How to find the k-th level of the tree? Root = 2 is zero. S. language