Solution to level 12 in Untrusted: http://alex.nisnevich.com/untrusted/

untrusted-lvl12-solution.js

/*
 * robotNav.js
 *
 * The green key is located in a slightly more
 * complicated room. You'll need to get the robot
 * past these obstacles.
 */

function startLevel(map) {
    // Hint: you can press R or 5 to "rest" and not move the
    // player, while the robot moves around.

    map.placePlayer(0, map.getHeight() - 1);
    var player = map.getPlayer();

    map.defineObject('robot', {
        'type': 'dynamic',
        'symbol': 'R',
        'color': 'gray',
        'onCollision': function (player, me) {
            me.giveItemTo(player, 'greenKey');
        },
        'behavior': function (me) {
       		if (typeof this.backtrack == 'undefined') {
            	var $ = this;
            	this.backtrack = [];
                this.visited = {};
                this.p = {x: 1, y: 1};
                this.getPosDiff = function(dir) {
                	if (dir == 'center')
                    	return {x: 0, y: 0};
                    if (dir == 'right')
                    	return {x: 1, y: 0};
                    if (dir == 'left')
                    	return {x: -1, y: 0};
                    if (dir == 'up')
                    	return {x: 0, y: -1};
                    if (dir == 'down')
                    	return {x: 0, y: 1};
                };
                this.reverse = { 
                	'up': 'down','down': 'up',
                    'left': 'right','right': 'left'};
                this.move = function (dir) {
                    var d = $.getPosDiff(dir);
                    $.p.x += d.x;
                    $.p.y += d.y;
                   	me.move(dir);
                    $.backtrack.push($.reverse[dir]);
                };
                this.moveBack = function() {
                	var dir = $.backtrack.pop();
                	var d = $.getPosDiff(dir);
                    $.p.x += d.x;
                    $.p.y += d.y;
                    me.move(dir);
                }
                this.visit = function () { 
                	var cur = $.p.x+','+$.p.y;
                	$.visited[cur] = true;
                }
                this.canMove = function (dir) {
                	var d = $.getPosDiff(dir);
                    var next = ($.p.x+d.x)+','+($.p.y+d.y);
                    return !(next in $.visited) && me.canMove(dir);
                }
            }
            
            this.visit();
            if (this.canMove('right'))
            	this.move('right');
            else if (this.canMove('down'))
            	this.move('down');
            else if (this.canMove('left'))
            	this.move('left');
            else if (this.canMove('up'))
            	this.move('up');
            else {
                this.moveBack();
            }
        }
    });

    map.defineObject('barrier', {
        'symbol': '░',
        'color': 'purple',
        'impassable': true,
        'passableFor': ['robot']
    });

    map.placeObject(map.getWidth() - 1, map.getHeight() - 1, 'exit');
    map.placeObject(1, 1, 'robot');
    map.placeObject(map.getWidth() - 2, 8, 'greenKey');
    map.placeObject(map.getWidth() - 2, 9, 'barrier');

    for (var x = 0; x < map.getWidth(); x++) {
        map.placeObject(x, 0, 'block');
        if (x != map.getWidth() - 2) {
            map.placeObject(x, 9, 'block');
        }
    }

    for (var y = 1; y < 9; y++) {
        map.placeObject(0, y, 'block');
        map.placeObject(map.getWidth() - 1, y, 'block');
    }

    for (var i = 0; i < 4; i++) {
        map.placeObject(20 - i, i + 1, 'block');
        map.placeObject(35 - i, 8 - i, 'block');
    }
}

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

function onExit(map) {
    if (!map.getPlayer().hasItem('greenKey')) {
        map.writeStatus("We need to get that key!");
        return false;
    } else {
        return true;
    }
}