Solution to level 17 in Untrusted: http://alex.nisnevich.com/untrusted/

untrusted-lvl17-solution.js

/***************
 * pointers.js *
 ***************
 *
 * You! How are you still alive?
 *
 * Well, no matter. Good luck getting through this
 * maze of rooms - you'll never see me or the Algorithm again!
 */

function startLevel(map) {
    function shuffle(o){ //v1.0 [http://bit.ly/1l6LGQT]
        for(var j, x, i = o.length; i; j = Math.floor(Math.random() * i),
            x = o[--i], o[i] = o[j], o[j] = x);
        return o;
    };

    map.createFromGrid(
        ['+++++++++++++++++++++++++++++++++++++++++++++',
         '++o *++++o *++++o *++++o *++++o *++++o *+++++',
         '+* @ o++*   o++*   o++*   o++*   o++*   o++++',
         '++o *++++o *++++o *++++o *++++o *++++o *+++++',
         '+++++++++++++++++++++++++++++++++++++++++++++',
         '+++++* o++++* o++++* o++++* o++++* o++++* o++',
         '++++o   *++o   *++o   *++o   *++o   *++o   *+',
         '+++++* o++++* o++++* o++++* o++++* o++++* o++',
         '+++++++++++++++++++++++++++++++++++++++++++++',
         '++o *++++o *++++o *++++o *++++o *++++o *+++++',
         '+*   o++*   o++*   o++*   o++*   o++*   o++++',
         '++o *++++o *++++o *++++o *++++o *++++o *+++++',
         '+++++++++++++++++++++++++++++++++++++++++++++',
         '+++++* o++++* o++++* o++++* o++++* o++++* o++',
         '++++o   *++o   *++o   *++o   *++o   *++o   *+',
         '+++++* o++++* o++++* o++++* o++++* o++++* o++',
         '+++++++++++++++++++++++++++++++++++++++++++++',
         '++o *++++o *++++o *++++o *++++o *++++o *+++++',
         '+*   o++*   o++*   o++*   o++*   o++* E o++++',
         '++o *++++o *++++o *++++o *++++o *++++o *+++++',
         '+++++++++++++++++++++++++++++++++++++++++++++'],
        {
            '@': 'player',
            'E': 'exit',
            '+': 'block',
            'o': 'teleporter',
            '*': 'trap',
        }, 2, 2);

    var canvas = map.getCanvasContext();

    var teleportersAndTraps = map.getDynamicObjects();
    teleportersAndTraps = shuffle(teleportersAndTraps);

    for (i = 0; i < teleportersAndTraps.length; i+=2) {
        var t1 = teleportersAndTraps[i];
        var t2 = teleportersAndTraps[i+1];

        // Point each teleporter to either another teleporter
        // or a trap
        if (t1.getType() == 'teleporter') {
            t1.setTarget(t2);
        }
        if (t2.getType() == 'teleporter') {
            t2.setTarget(t1);
        }

        var exit = t1.findNearest('exit');
        var cells = map.getAdjacentEmptyCells(exit.x, exit.y);
        var cell = {
            x: cells[0][0][0],
            y: cells[0][0][1]
        };
        
        map.placeObject(cell.x, cell.y, 'teleporter');
        console.log(cell);
        
        var teleportersAndTrapsOriginal = map.getDynamicObjects();
        
        var len = teleportersAndTrapsOriginal.length;
        var target = teleportersAndTrapsOriginal[len-1];
        
        for (i = 0; i < teleportersAndTrapsOriginal.length-1; i++) {
            var t = teleportersAndTrapsOriginal[i];
            if (t.getType() == 'teleporter') {
                t.setTarget(target);
            }
           }
           
            
        break;
        /*
        var i = 0;
        var j;
        var teleportersAndTrapsOriginal = map.getDynamicObjects();
        var firstTeleporter, lastTeleporter;
        
        while (i < teleportersAndTrapsOriginal.length) {
              t1 = teleportersAndTrapsOriginal[i];
            console.log(t1.findNearest('exit'));
            i++;
            if (t1.getType() != 'teleporter') continue;
            
            if (!firstTeleporter) firstTeleporter = t1;
            
            j = i;
            while (j < teleportersAndTrapsOriginal.length) {
                t2 = teleportersAndTrapsOriginal[j];
                if (t2.getType() == 'teleporter') break;
                j++;
            }
                
            lastTeleporter = t2;
            i = j;
            
            t1.setTarget(t2);
            console.log(t1, 'set target on', t2);
        }
        
        lastTeleporter.setTarget(firstTeleporter);
        
        break;*/
        
    }
}

function validateLevel(map) {
    map.validateExactlyXManyObjects(1, 'exit');
}