andreytim

import java.util.*;

public class LetterCombinations {

    private static final Map<Character, String> mapping = new HashMap<>();
    static {
        mapping.put('2', "abc"); mapping.put('3', "def"); mapping.put('4', "ghi");
        mapping.put('5', "jkl"); mapping.put('6', "mno"); mapping.put('7', "pqrs");
        mapping.put('8', "tuv"); mapping.put('9', "wxyz");
    }

andreytim

def mce_BK(R, P, X, g, cliques):
    if not P and not X:
        cliques.append(R)
    for v in degeneracy_ordering(P, g):
        mce_BK(R | set([v]), P & g.neighbors(v), X & g.neighbors(v), 
                g, cliques)
        P.remove(v)
        X.add(v)

def degeneracy_ordering(P, g):