sorting tournament seeds

Question

I\'m making a HTML/JS powered single/double elimination bracket web app. I am struggling to figure out how to assign the first round matches from a list of seeded teams/players.

Answer 1

This is probably not as efficient as @alex's answer using a custom sort function, but certainly easier to write and understand:

// This algorithm assumes that seeds.length is an even number
var seeds = [1, 2, 3, 4, 5, 6, 7, 8],
    firstRound = [];

while (seeds.length)
{
    firstRound.push(seeds.shift());
    firstRound.push(seeds.pop());
}

// seeds is now empty
// firstRound is now [1, 8, 2, 7, 3, 6, 4, 5]

Demo 1

---

Actually, I just thought of a faster algorithm (in-place "sorting", takes O(n) time):

// Also assumes that seeds.length is an even number
var seeds = [1, 2, 3, 4, 5, 6, 7, 8],
    numSeeds = seeds.length,
    stop = numSeeds >> 1,
    temp;

for (var i=1; i

Demo 2

Note that neither of these algorithms generates exactly the same order of pairs as in the OP, but they both generate the same set of pairs:

• (1,8)
• (2,7)
• (3,6)
• (4,5)