Elevator Saga - An Addictive Programming Challenge
Written by Mike James
Monday, 26 January 2015

Elevators are simple - right? They just go up and down and move people. But if you are a programmer, waiting for one can prompt the thought.could this be done better? The Elevator Saga is a game where you get to schedule their movements. It isn't easy and it is addictive.

This is a nice JavaScript simulation of transporting people using one or more elevators. You write the code and the elevators move accordingly. So, for example, the initial program supplied to get you started reads:

`{ init: function(elevators, floors) {  var elevator = elevators[0];    // Let's use the first  elevator  elevator.on("idle", function() {   // The elevator is idle,   // so let's go to all the floors   ``     //(or did we forget one?)  elevator.goToFloor(0);  elevator.goToFloor(1);  }); }, update: function(dt, elevators, floors) { // We normally don't need to do anything here }}`

You supply two functions init, which is called just once at the start; and update, which is called repeatedly. This simple algorithm just sends the elevator to each floor in turn collecting and dropping off passengers.

This algorithm is flawed, as mentioned in the comments, because there are thee floors not just two. The algorithm fails as the elevator slowly clogs up with people needing to get off at the second floor.

You are challenged to improve the algorithm to transport the requisite number of people in the given time and when you succeed you can move on to the next challenge. There are no prizes but the intrinsic reward is in showing that you can invent an algorithm that works. It would also be a possible way of introducing someone to programming but only with some additional help.

Notice that the passengers don't indicate to the elevator the floor they want to get to just up or down. In real life entering an elevator without floor buttons is worrying to passengers so it tends not to be used but it is efficient.

The question is how efficient?

Later on you get to work with multiple elevators as well and then it gets really interesting.

You can discover the full API that you can use in constructing an algorithm on the challenge web site, but if you are interested in some theory Sharpen your Coding Skills - Elevator Puzzle to find out about Karp's Algorithm.

Elevator Saga

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