Consider a lift lobby where people are waiting for the lift. Now when lift arrives people get in irrespective of who came first. Thus, the person who came first keeps waiting and others keep getting in. Design a lift system which can solve the problem of this person.

Question

Anonymus (One who posted this question) · Accepted Answer

I don't find any of the answers posted above by Vikram, Vishnu or Deb as appropriate!

@Vikram: Can you increase the size of a lift lobby??? FYI a lift lobby is the space u generally have between an array of lifts located on opposite sides of a wall. Having a narrow path and having a long waiting queue?? Imagine such a situation in an office or a shopping mall or an apartment! and will u demolish an existing building to reinstall this design u are suggesting - who will buy ur design?
@Vishnu: Elevator - do u mean escalator? Imagine a 30-40 floor building and and escalator going 30 floors up and down! Think of the time u will have to take to reach the top floor. There can be n types of solution, but it is important to evaluate every solution. we are not suggesting just an alternate solution, but addressing the users problem. I think we are increasing his problem by this design. And also consider the technical feasibility of such design in say 50 floor building? and again will u demolish an existing building to reinstall this design u are suggesting - who will buy ur design?
@Deb: Again, we are solving the users problem here and not just suggesting solution for the sake of it. Imagine such a lift system installed in your apartment complex! The camera would know that you are no. 7, how would you know that? not knowing this you will try to enter a lift and then u say that the lift will stop u!!! and there may be 6 lifts in the lobby. Say at a particular instance of time 2 lifts - lift 1 (going down) and lift 4 (going up) arrive. you will not let in person no 10 who wants to go down while all other 9 who came before and wants to go up. And how would the camera know which floor the person wants to go??

I am just giving pointers and this is the way the options will be struck down, if they do not address the actual problem/ or you do not consider the feasibility of implementation. 

The solution that i gave was this:
When one enters a lift lobby first thing he does is to press up or down button to call a lift going up or down respectively. Once we enter a lift we have the keyboard to press the floor number inside the lift. 
What i suggested is to have a similar keyboard somewhere at the entrance of the lift lobby along with a small embedded display screen. So that when i am entering the lobby i press say 11 (to go to the 11th floor). While i press that, instantly the lobby  shows me the lift number (say Lift 1, 2, ..6) i need to get into. So i know which lift i need to get into and i will obviously stand in front of that lift. At any time, the same lift number will not be issued to more than X people (where X is a predefined number of persons who can go in a lift at a time). 
Here the design is not in reinventing the entire lift system. Nobody will incur so much real estate cost to scrap the existing lift system and build a totally new designed one!
The actually design here would be to build the backend logic that the lift system would use to assign the right lift number to every arriver in the most efficient way. 

e.g. Assume a simple start state (for a 2 lift lobby) when all lifts are stationary at the ground floor. When P1 (going to F10) comes System assigns him L1. For P2 (F5) assigns L2. Now to P3 (F12) assign L1, P4(F11) assign L1, P5(F4) assign L2 and so on. This is a simple situation. All we need is an algorithm which can address this lift assignment in the most efficient way.

I WAS SELECTED :)

vikram · Answer

increase the load capacity of lobby by its size andhaving a narrow path in front of lobby  so that the person who came first can only enter first, just like we stand for ticket in railway station.

Parthiban Rangaraj · Answer

Sorry for my previous response. Wrongly understood the question

Boris · Answer

The lift system you described is one they use in a large hospital close to where I live. I think they did it so that you would not have to press buttons inside the lift and not for the particular problem described in the question.

Parthiban Rangaraj · Answer

Have a two way door opening in the lift. But always entry should be in one side and exit other side.

Prateek · Answer

@Anonymus (One who posted this question): I see two major flaws in this solution. 1) If a group of people wants to go to the same floor together and only person among the group presses the button, then the lift under this system would assume that only one person would enter and allot only 1 person's capacity to the entire group, thus exceeding the capacity frequently. Under this system, every individual would have to press the button even if they come together which is a bit of an inconvenience I feel. 2) Also, if someone presses the button, is allocated a lift and then doesn't enter, then the lift wont know and will not 'free' the capacity leading to it running under-capacity when there are other people waiting to use the lift.

Sigiloso · Answer

increase the no of lifts to serve for peak periods. Decrease the width of lift doors. enhance the lift algorithm to serve better.
Try to control the flow, by analyzing  the causes. 

Keep a notice board or appoint a security , if required.

Vish · Answer

Create a queuing system with barricades, just like at airport ticketing counters.

Sdeepika · Answer

Form a que..so that the person arrive first will be standing in front and enters the lift first

-_- · Answer

What's the problem here i can't find it ?

sridhar · Answer

It was not mentioned i the question that there are several lifts in th lobby. Hence, it a very simple solution for the first person to enter first is to arrange a baricade- Q system. Thats it....age old and very simple, price less solution.

Sigiloso · Answer

One way can be to have a id card scanner installed in the lift area. Since it is an office it is safe to assume that people will be having their id cards. When people come to the lift they scan their id cards, there can be a tv screen next to the lift which can show the order in which people have arrived.

Sigiloso · Answer

In my view , This is not any technical issue we are trying to solve, problem is rooted through people discipline. Install cc cam and publish few lift lobby disciplines, make sure  violation of rules  will be consider as HR escalation.
I am sure this problem will be corrected without any huge technology investment.
With this approach two benefit I can see :
Huge R&D investment can be saved.
If we could correct People behaviours that will be a permanent fix for the many other initiatives.

If the question is asked to measure a person's reasoning and interviewer expecting a solution through some logical technology initiation , selected candidate has given a reasonable answer of course a complex algorithm need to be develop with all permutations and combinations along with pros and cons, still it is possible through embedded technology.

Sigiloso · Answer

It’s simple guys, keep one notice FCFS 👍🏻

SP · Answer

IMO there should be a token vending machine just outside the lift where as and when people come, take out token. Now these tokens are embedded with a single chip with a kind of dynamic number saved on them. The vending machine would draw out tokens in a numeric sequence, once a person enters a life he would have to punch/drop his token into a reading device which will open the gate for the lift in a particular order. Once all are done, the machine would be reset and again the procedure can be repeated for the next set of people. This is something similar to Metro Train Tokens.

Vishnu · Answer

a.)If you are talking about the technical customization, HAVE A ELEVATOR INSTEAD OF LIFT.

Regards
Vishnu
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