This function obtains the node levels from a tree.
Arguments
- adj_list
The adjacency list of the tree.
Value
It returns a vector of integers. The length of this vector will be
the number of nodes in the tree. The root is at level 1, the next is at level
2, and so on.
Details
This function is used to check if the specification of the tree is
in BFS order. If that is indeed the case, the levels of each node should be
sorted.
This function is not exported for the general user.
