My solution to Elevator Saga

{
    /* This is my (Joel Yliluoma's) solution to Elevator Saga at http://play.elevatorsaga.com/ */
    /* This code plows through all challenges from #1 to #17. However, note:
     * In challenge #6, you need to change one of the for-loops, below. (Indicated in comments.)
     * In the max-wait challenges, you may need to click Restart a few ones to get better luck.
     */
    /* Check out my programming-related YouTube channel! http://youtube.com/user/Bisqwit */

    init: function(elevators, floors) {
        var bot=999, top=-1, upOrder={}, dnOrder={}, age={}, totalage=1;

        floors.forEach(function(f) {
            var fn = f.floorNum();
            // Find top and bottom floors
            if(fn > top) top = fn;
            if(fn < bot) bot = fn;
            f.on("up_button_pressed",   function() { upOrder[fn] = fn; } );
            f.on("down_button_pressed", function() { dnOrder[fn] = fn; } );
            age[fn] = 0;
        });

        //elevators.pop(); // Uncomment for challenge #6
        elevators.forEach(function(e) {
            var curdir=0;
            e.goingUpIndicator(true);
            e.goingDownIndicator(true);
            e.pOrder = {};
            // goTo: Register a new target
            e.goTo  = function(f, now) {
                var cur = e.currentFloor();
                //console.log("goto " + f, pOrder,dnOrder,upOrder);
                if(f != cur) { if(f < cur) curdir=-1; else curdir=1; }
                e.goToFloor(f, now);
                // There's a promise we will go to this floor, so delete it
                delete e.pOrder[f];
                delete upOrder[f];
                delete dnOrder[f];
            };
            e.on("floor_button_pressed", function(num){ e.pOrder[num]=num; });
            e.on("passing_floor", function(f,dir) {
                if(e.pOrder[f] || (e.loadFactor() < 0.3 && (
                                  (/*dir=="up" &&*/ upOrder[f])
                               || (/*dir=="down" &&*/ dnOrder[f]) )))
                {
                    e.goTo(f, true);
                }
            });
            e.on("stopped_at_floor", function(f) {
                // Are we at top floor? We are going down next.
                var cur = e.currentFloor();
                if(cur == top) curdir = -1;
                if(cur == bot) curdir = 1;
                // We have arrived at this floor.
                age[f] = ++totalage;
            });
            e.on("idle", function(){
                var cur = e.currentFloor(),  bestscore=top*2, target = -1;//Math.floor(Math.random() * (top+1));
                //console.log("cur="+cur, pOrder);
                // Pick a target. Check each floor first.
                var orders = [e.pOrder,upOrder,dnOrder];
                if(e.loadFactor() >= 0.02) orders = [e.pOrder]; // too full
                for(var oi in orders) for(var order in orders[oi])
                {
                    if(order == cur) { continue; } // Ignore requests to go to the same floor...
                    // The score (really penalty) is the distance to the current floor
                    var score = Math.abs(order - cur) + (age[order]-totalage);
                    //if(curdir != 0 && (curdir > 0) != (order > cur)) score += totalage; // Orders to change direction are ranked low

                    // If we don't have any passengers, downrank floors that _other_ elevators are heading towards
                    if(e.pOrder.length == 0)
                        for(var ei in elevators)
                            if(elevators[ei].pOrder[order])
                            {
                                // What is the probility the other elevator will head to this floor _next_?
                                var unprob = Math.abs(order - elevators[ei].currentFloor()) + elevators[ei].pOrder.length;
                                score += top/unprob;
                            }

                    if(score < bestscore) { bestscore=score; target=order; }
                }
                // Now get the highest ranking candidate, and honor it.
                if(target == -1) { e.goTo(cur, true); return; } // This will just re-launch the "idle" code
                /* There is one special case that needs to be worked on.
                 * Suppose one elevator is empty and decides to go
                 * towards a floor to pick up passengers (based on upOrder/dnOrder).
                 * Now there's another elevator that has passengers who want to leave
                 * at that same floor (its pOrder), but he's still busy heading to another floor.
                 * There's a high chance both elevators will rush to the same floor at the same time.
                 */
                e.goTo(target);
            });
        });
    },
    update: function(dt, elevators, floors) {
        // We normally don't need to do anything here
    }
}