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);
        }

        // TODO find a way to remove the API docs
        // wouldn't want the 'good doctor' to find
        // out about map.getCanvasCoords()...
           var maxY = 0;
        for (var j = 0; j < teleportersAndTraps.length; ++j) {
          var tt = teleportersAndTraps[j];
          if (tt.getType() != 'teleporter') {
            continue;
          }
          var ttc = map.getCanvasCoords(tt);
          if (ttc.y >= maxY) {
             maxY = ttc.y;
          }
        }
        
        var maxX = 0;
        var maxT = null;
		for (var j = 0; j < teleportersAndTraps.length; ++j) {
          var tt = teleportersAndTraps[j];
          if (tt.getType() != 'teleporter') {
          	continue;
          }
          var ttc = map.getCanvasCoords(tt);
          if (ttc.y == maxY && ttc.x >= maxX) {
             maxX = ttc.x;
             maxT = tt;
          }
        }        
        
        if (t1.getType() == 'teleporter' && t1 != maxT) {
          t1.setTarget(maxT);
          var t1c = map.getCanvasCoords(t1);	
          canvas.beginPath();
		  canvas.moveTo(t1c.x, t1c.y);
          canvas.lineTo(maxX, maxY);
          canvas.lineWidth = 2;
          canvas.strokeStyle = '#fff';
          canvas.stroke();
		}
        if (t2.getType() == 'teleporter' && t2 != maxT) {
          t2.setTarget(maxT);
          var t2c = map.getCanvasCoords(t2);
          canvas.beginPath();
		  canvas.moveTo(maxX, maxY);
          canvas.lineTo(t2c.x, t2c.y);
          canvas.lineWidth = 2;
          canvas.strokeStyle = '#fff';
          canvas.stroke();
        }




    }
}

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