1 d = [['D',5],['B',6],['A',4],['C',0],['B',3],['D',1],['E',-1]] 2 t = h = 2 3 p = d[h][1] 4 while p != -1: 5 d[t][1] = p 6 k = p 7 q = d[p][1] 8 while q != -1: 9 if d[p][0] != d[q][0]: 10 d[k][1] = q 11 k = q 12 else: 13 d[t][1] = d[p][1] 14 q = d[q][1] 15 if d[t][1] == p: 16 t = p 17 p = d[p][1]