q1

def d(s):
    raw_input("----DEBUG----{0}".format(s))

class City:
    # parses the intersections from a string s
    def __init__(self, s):
        nums = s.split()
        self.juncs = set(map(int,nums))

        self.roads = dict()

        for i in range(0, len(nums), 2):
            if int(nums[i]) in self.roads:
                self.roads[int(nums[i])].append(int(nums[i+1]))
            else:
                self.roads[int(nums[i])] = [int(nums[i+1])]

    def paths(self, a, b, current_path=[]):
        # IF
        #   the start point and end point are the same at the beginning,
        #   junction 'a' does not exist
        #   junction 'b' does not exist
        #   there are not outgoing roads from 'a'
        # return nothing
        if (current_path == [] and a == b) or a not in self.juncs or b not in self.juncs or not self.roads.has_key(a):
            return []

        # add the starting junction to the path
        current_path = current_path + [a]

        # If we've reached the endpoint,
        if a == b:
            return [current_path]

        # prepare the return
        thispath = []

        # for every junction reachable from a
        for junction in self.roads[a]:
            # if we haven't already visited this junction,
            if junction not in current_path:
                # send out a probe finding all paths from this junction to the ending point
                probe = self.paths(junction, b, current_path)
                # add all the paths found
                for potential_path in probe:
                    thispath.append(potential_path)

        # return the paths found from junction a to junction b
        return thispath

# takes an input string and returns a list of Cities
def parse(s):
    print "p"

t =  City("0 1  0 2  0 4  2 4  2 3  3 1  4 3")

print t.paths(0,3)