Please provide a hint regarding what algorithm to use for the following problem: Given an undirected graph of N nodes and M edges find the maximum size of a subgraph of the graph such that the degree of each node is greater than equal to A and degree of each node is less than equal to K - B. Here K refers to the size of the subgraph and A and B are supplied in the input.

This is an Australian Informatics Olympiad question (with other details involving the theme that I have removed). Subtasks 1 worth 50 marks is for b = 0 which can be done using greedy approach. Hints for the general please.