Question

I’ve been struggling for quite a long time on this problem. This is a follow-up question on this answer (How to divide x number of players into 2 teams randomly multiple times, differently every time?).

So, I have x number of players, and for each I give 1 << n mask value. By using those masks I can easily form a match with 2 players in each team. Now, if total number of players is 5, one possible match could be like this:

01100 team a
00011 team b
------------
10000 player resting

or with 6 players it could look like this:

100010 team a
001001 team b
-------------
000100 player resting
010000 player resting

Question
How can I get those resting players by comparing team a and team b masks together? (I’m a total bitwise noob so code examples are well appreciated)

Thanks

Answer 1

Do XOR on value of team A and B:

var resting = a ^ b;

Then resting players will be marked by 0, i.e:

100010 team a
001001 team b
-------------
101011 players resting

Finally, iterate through each bit of the result:

var totalPlayers = 6;

for (var i = 1; i <= totalPlayers; i++) {

   if ((resting & 1) === 0) {
       console.log("Player #" + i + " is resting.");
   }

   resting >>>= 1;
}

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Here’s live example: http://ideone.com/Kb3XJ (in Java, not JavaScript, but that’s not the issue)