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);
        }

    } // end for loop
        
    
    // find a teleporter that is in the bottom right corner...
    // remember location in array:
    var teleDestList = [];
    
    var destmin = {
      x: 36,
      y: 18,
    }
    
    for (i = 0; i < teleportersAndTraps.length; i+=1) {
      var tele = teleportersAndTraps[i];
      if (tele.getType() == 'teleporter') {
        //var pos = map.getCanvasCoords(tele);
        if ( (tele.getX() > destmin.x) &&
            (tele.getY() > destmin.y) ) {
          teleDestList.push(i);
        }
      }
    }
      
      var teleDest = teleDestList[0];
    
    // highlite target
    map.setSquareColor(
      teleportersAndTraps[teleDest].getX(),
      teleportersAndTraps[teleDest].getY(),
      '#9b0');
    
    // now set all teleporters to the same target:
    for (i = 0; i < teleportersAndTraps.length; i+=1) {
         var tele = teleportersAndTraps[i];
        // set all teleporters to the special target.
        if (tele.getType() == 'teleporter') {
            if (tele == teleportersAndTraps[teleDest] ) {
                //handle self reference
                tele.setTarget(teleportersAndTraps[teleDestList[1]]);
            } else {
                  tele.setTarget(teleportersAndTraps[teleDest]);
            }   
        }
    } 
    
    
    // make some lines to see the connections
    for (i = 0; i < teleportersAndTraps.length; i+=2) {
        var t1 = teleportersAndTraps[i];
        var t2 = teleportersAndTraps[i+1];
        
        /**/
        // only draw lines if both sides are teleporters
        if ( (t1.getType() == 'teleporter') &&
             (t2.getType() == 'teleporter') )
        {
            var start = map.getCanvasCoords(t1);
            var end = map.getCanvasCoords(t2);
            
            // using canvas to draw the line
            var ctx = map.getCanvasContext();
            ctx.beginPath();
            ctx.strokeStyle = 'white';
            ctx.lineWidth = 1;
            ctx.moveTo(start.x, start.y);
            ctx.lineTo(end.x, end.y);
            ctx.stroke();
         }
       /**/
        
    }
}

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