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()...
        
        if (t1.getType() == 'teleporter' && t2.getType() == 'trap') {
        	var coords = map.getCanvasCoords(t1);
            var ctx = map.getCanvasContext();
            ctx.beginPath();
            ctx.strokeStyle = 'red';
            ctx.lineWidth = 5;
            ctx.moveTo(coords.x - 10, coords.y - 10);
            ctx.lineTo(coords.x + 10, coords.y + 10);
            ctx.stroke();
            var ctx = map.getCanvasContext();
            ctx.beginPath();
            ctx.strokeStyle = 'red';
            ctx.lineWidth = 5;
            ctx.moveTo(coords.x + 10, coords.y - 10);
            ctx.lineTo(coords.x - 10, coords.y + 10);
            ctx.stroke();
        }
        
        if (t2.getType() == 'teleporter' && t1.getType() == 'trap') {
        	var coords = map.getCanvasCoords(t2);
            var ctx = map.getCanvasContext();
            ctx.beginPath();
            ctx.strokeStyle = 'red';
            ctx.lineWidth = 5;
            ctx.moveTo(coords.x - 10, coords.y - 10);
            ctx.lineTo(coords.x + 10, coords.y + 10);
            ctx.stroke();
            var ctx = map.getCanvasContext();
            ctx.beginPath();
            ctx.strokeStyle = 'red';
            ctx.lineWidth = 5;
            ctx.moveTo(coords.x + 10, coords.y - 10);
            ctx.lineTo(coords.x - 10, coords.y + 10);
            ctx.stroke();
        }
    }
}

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