texts = [['a','a','b'], ['a','a','a','b','b','c'], ['b','a','b'], ['a','c','a','b','a','b']]

for text in texts:

    highest = 1
    thing = {highest: []}

    for t in text:
        found = False
        for h in xrange(highest, 0, -1):
            if h == 0:
                continue
            for x in thing[h]:
                if found:
                    break
                if x == t:
                    found = True
                    if highest == h:
                        highest+=1
                        thing[highest] = []
                    thing[h+1].append(t)

            if found:
                while t in thing[h]:
                    thing[h].remove(t)
                    thing[h+1].append(t)

        if not found:
            thing[1].append(t)

    print thing