I am using JavaScript to work out all the combinations of badminton doubles matches from a given list of players. Each player teams up with everyone else.

EG. If I have the following players a, b, c & d. Their combinations can be:

a & b V c & d

a & c V b & d

a & d V b & c

I am using the code below, which I wrote to do the job, but it's a little inefficient. It loops through the PLAYERS array 4 times finding every single combination (including impossible ones). It then sorts the game out into alphabetical order and stores it in the GAMES array if it doesn't already exist. I can then use the first half of the GAMES array to list all game combinations.

The trouble is if I have any more than 8 players it runs really slowly because the combination growth is exponential.

Does anyone know a better way or algorithm I could use? The more I think about it the more my brain hurts!

var PLAYERS = ["a", "b", "c", "d", "e", "f", "g"];
var GAMES = [];

var p1, p2, p3, p4, i1, i2, i3, i4, entry, found, i;
var pos = 0;
var TEAM1 = [];
var TEAM2 = [];

// loop through players 4 times to get all combinations
for (i1 = 0; i1 < PLAYERS.length; i1++)
{
    p1 = PLAYERS[i1];
    for (i2 = 0; i2 < PLAYERS.length; i2++)
    {
        p2 = PLAYERS[i2];
        for (i3 = 0; i3 < PLAYERS.length; i3++)
        {
            p3 = PLAYERS[i3];
            for (i4 = 0; i4 < PLAYERS.length; i4++)
            {
                p4 = PLAYERS[i4];

                if ((p1 != p2 && p1 != p3 && p1 != p4) &&
                   (p2 != p1 && p2 != p3 && p2 != p4) &&
                   (p3 != p1 && p3 != p2 && p3 != p4) &&
                   (p4 != p1 && p4 != p2 && p4 != p3))
                {
                    // sort teams into alphabetical order (so we can compare them easily later)
                    TEAM1[0] = p1;
                    TEAM1[1] = p2;
                    TEAM2[0] = p3;
                    TEAM2[1] = p4;
                    TEAM1.sort();
                    TEAM2.sort();

                    // work out the game and search the array to see if it already exists
                    entry = TEAM1[0] + " & " + TEAM1[1] + " v " + TEAM2[0] + " & " + TEAM2[1];
                    found = false;
                    for (i=0; i < GAMES.length; i++)
                    {
                        if (entry == GAMES[i]) found = true;
                    }

                    // if the game is unique then store it
                    if (!found)
                    {
                        GAMES[pos] = entry;
                        document.write((pos+1) + ": " + GAMES[pos] + "<br>");
                        pos++;
                    }
                }
            }
        }
    }
}

Thanks in advance.

Jason.