Solution for https://community.topcoder.com/stat?c=problem_statement&pm=7587 . A pain in the ass...

bags_quiz.py

import re

PUT_PATTERN = re.compile(r'PUT (?P<what>[0-9]+) INSIDE (?P<to>[0-9]+)')
LOOSE_PATTERN = re.compile(r'SET (?P<which>[0-9]+) LOOSE')
SWAP_PATTERN = re.compile(r'SWAP (?P<one>[0-9]+) WITH (?P<other>[0-9]+)')


class Bag(object):
    def __init__(self, n, parent=None):
        self.n = n
        self.contains = set()
        self.parent = parent

    @property
    def correct(self):
        return all([el.n < self.n for el in self.contains])

    def remove(self, bag):
        self.contains.remove(bag)

    def add(self, bag):
        bag.parent = self
        self.contains.add(bag)

    def __str__(self):
        return "%s - %s" % (self.n, list(self.contains))

    __repr__ = __str__
            

class BagsQuiz(object):
    def checkIfProper(self, n, actions):
        self.good = True
        self.floor = Bag(0)
        self.bags = [Bag(i + 1, self.floor) for i in xrange(n)]
        self.floor.contains = set(self.bags)


        for action in actions:
            m = PUT_PATTERN.match(action)
            if m is not None:
                what = int(m.group('what')) - 1
                to = int(m.group('to')) - 1
                self.put(what, to)
                print "action: %s, result: %s" % (action, self.floor)
                continue
            m = LOOSE_PATTERN.match(action)
            if m is not None:
                which = int(m.group('which')) - 1
                self.loose(which)
                print "action: %s, result: %s" % (action, self.floor)
                continue
            m = SWAP_PATTERN.match(action)
            if m is not None:
                one = int(m.group('one')) - 1
                other = int(m.group('other')) - 1
                self.swap(one, other)
            print "action: %s, result: %s" % (action, self.floor)
                
        if not self.good or not all([bag.correct for bag in self.bags]):
            return -1
        else:
            return len(self.floor.contains)

    def put(self, what, to):
        wbag = self.bags[what]
        tbag = self.bags[to]
        if wbag.parent == self.floor and tbag.parent == self.floor:
            wbag.parent.remove(wbag)
            tbag.add(wbag)
        else:
            self.good = False

    def loose(self, which):
        cbag = self.bags[which]
        if cbag.parent == self.floor:
            for el in cbag.contains:
                self.floor.add(el)
            cbag.contains = set()
        else:
            self.good = False

    def swap(self, one, other):
        bag1 = self.bags[one]
        bag2 = self.bags[other]
        if bag1.parent == self.floor and bag2.parent == self.floor:
            bag_list1 = list(bag1.contains)
            bag_list2 = list(bag2.contains)
            for bag in bag_list1:
                bag1.remove(bag)
                bag2.add(bag)
            for bag in bag_list2:
                bag2.remove(bag)
                bag1.add(bag)
        else:
            self.good = False


if __name__ == "__main__":
    n = 3
    actions = ["PUT 1 INSIDE 2", "PUT 3 INSIDE 1"]
    bq = BagsQuiz()
    print bq.checkIfProper(n, actions)