Generate Round Robin Schedule with Balanced Home/Away in Python

round-robin.py

def create_balanced_round_robin(players):
    """ Create a schedule for the players in the list and return it"""
    s = []
    if len(players) % 2 == 1: players = players + [None]
    # manipulate map (array of indexes for list) instead of list itself
    # this takes advantage of even/odd indexes to determine home vs. away
    n = len(players)
    map = list(range(n))
    mid = n // 2
    for i in range(n-1):
        l1 = map[:mid]
        l2 = map[mid:]
        l2.reverse()
        round = []
        for j in range(mid):
            t1 = players[l1[j]]
            t2 = players[l2[j]]
            if j == 0 and i % 2 == 1:
                # flip the first match only, every other round
                # (this is because the first match always involves the last player in the list)
                round.append((t2, t1))
            else:
                round.append((t1, t2))
        s.append(round)
        # rotate list by n/2, leaving last element at the end
        map = map[mid:-1] + map[:mid] + map[-1:]
    return s

teams = ["Lions", "Tigers", "Bears", "Dorothy", "Toto"]
schedule = create_balanced_round_robin(teams)
print("\n".join(['{} vs. {}'.format(m[0], m[1]) for round in schedule for m in round]))

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