factor out of groupstage

.gitignore

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+node_modules

LICENSE

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+(The MIT License)
+
+Copyright (c) 2013 Eirik Albrigtsen
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+'Software'), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

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+# Round Robin [![Build Status](https://secure.travis-ci.org/clux/roundrobin.png)](http://travis-ci.org/clux/roundrobin) [![Dependency Status](https://david-dm.org/clux/roundrobin.png)](https://david-dm.org/clux/roundrobin)
+
+A simple round robin match scheduler to aid tournament implementations. The round robin implementation is [translated directly from the idea outlined on wikipedia](http://en.wikipedia.org/wiki/Round-robin_tournament#Scheduling_algorithm).
+
+## Usage
+Simply give the number of players (with an optional players array), and it will spit out the array of rounds necessary:
+
+```js
+var robin = require('roundrobin');
+robin(6);
+[ [ [ 1, 6 ], [ 2, 5 ], [ 3, 4 ] ],
+  [ [ 1, 5 ], [ 6, 4 ], [ 2, 3 ] ],
+  [ [ 1, 4 ], [ 5, 3 ], [ 6, 2 ] ],
+  [ [ 1, 3 ], [ 4, 2 ], [ 5, 6 ] ],
+  [ [ 1, 2 ], [ 3, 6 ], [ 4, 5 ] ] ]
+
+// or with names supplied
+robin(6, ['clux', 'lockjaw', 'pibbz', 'xeno', 'e114', 'eclipse']);
+[ [ [ 'clux', 'eclipse' ], [ 'lockjaw', 'e114' ], [ 'pibbz', 'xeno' ] ],
+  [ [ 'clux', 'e114' ], [ 'eclipse', 'xeno' ], [ 'lockjaw', 'pibbz' ] ],
+  [ [ 'clux', 'xeno' ], [ 'e114', 'pibbz' ], [ 'eclipse', 'lockjaw' ] ],
+  [ [ 'clux', 'pibbz' ], [ 'xeno', 'lockjaw' ], [ 'e114', 'eclipse' ] ],
+  [ [ 'clux', 'lockjaw' ], [ 'pibbz', 'eclipse' ], [ 'xeno', 'e114' ] ] ]
+```
+
+## Installation
+Install from npm:
+
+```bash
+$ npm install roundrobin --save
+```
+
+## License
+MIT-Licensed. See LICENSE file for details.

package.json

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+{
+  "name": "roundrobin",
+  "description": "A round-robin scheduler used in different tournaments",
+  "author": "Eirik Albrigtsen <analsandblaster@gmail.com>",
+  "version": "0.0.0",
+  "repository": {
+    "type": "git",
+    "url": "clux/roundrobin"
+  },
+  "keywords": ["round", "robin", "tournament"],
+  "main": "robin.js",
+  "scripts": {
+    "test": "tap test/*.js"
+  },
+  "dependencies": {},
+  "devDependencies": {
+    "interlude": "~1.0.2",
+    "tap": "~0.4.4"
+  },
+  "bugs": {
+    "url": "http://github.com/clux/roundrobin/issues"
+  },
+  "license": "MIT"
+}

robin.js

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+const DUMMY = -1;
+// returns an array of round representations (array of player pairs).
+// http://en.wikipedia.org/wiki/Round-robin_tournament#Scheduling_algorithm
+module.exports = function (n, ps) {  // n = num players
+  var rs = [];                  // rs = round array
+  if (!ps) {
+    ps = [];
+    for (var k = 1; k <= n; k += 1) {
+      ps.push(k);
+    }
+  }
+
+  if (n % 2 === 1) {
+    ps.push(DUMMY); // so we can match algorithm for even numbers
+    n += 1;
+  }
+  for (var j = 0; j < n - 1; j += 1) {
+    rs[j] = []; // create inner match array for round j
+    for (var i = 0; i < n / 2; i += 1) {
+      if (ps[i] !== DUMMY && ps[n - 1 - i] !== DUMMY) {
+        rs[j].push([ps[i], ps[n - 1 - i]]); // insert pair as a match
+      }
+    }
+    ps.splice(1, 0, ps.pop()); // permutate for next round
+  }
+  return rs;
+};

test/robin.test.js

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+var tap = require('tap')
+  , test = tap.test
+  , $ = require('interlude')
+  , robin = require('../');
+
+test("robin", function (t) {
+  $.range(20).forEach(function (n) {
+    var rs = robin(n);
+    var expected = ($.odd(n)) ? n : n-1;
+    t.equal(expected, rs.length, "correct number of rounds");
+
+    var pMaps = [];
+    $.range(n).forEach(function (p) {
+      pMaps[p] = [];
+    });
+
+    rs.forEach(function (rnd, r) {
+      t.equal(rnd.length, Math.floor(n/2), "number of matches in round "+ (r+1));
+
+      var plrs = $.flatten(rnd);
+      t.deepEqual(plrs, $.nub(plrs), "players listed only once per round");
+
+      // keep track of who everyone is playing as well
+      rnd.forEach(function (p) {
+        var a = p[0]
+          , b = p[1];
+        pMaps[a].push(b);
+        pMaps[b].push(a);
+      });
+    });
+
+    Object.keys(pMaps).forEach(function (p) {
+      var val = pMaps[p].sort($.compare());
+      var exp = $.delete($.range(n), Number(p));
+      // if this true, then each play all exactly once by previous test
+      t.deepEqual(val, exp, "player " + p + " plays every enemy");
+    });
+  });
+  t.end();
+});