I have a question here that states:
Let (d1, . . . , dn) be a weakly increasing sequence of non-negative integers (i.e., repetition is allowed), such that the sum of all the di is an even number. Show that it is possible to construct a graph with this degree sequence. (Hint: it might not be possible to do if the graph is required to be simple.)
Could anyone give me an idea of how to approach this problem? Thanks a lot.