CareerCup

Design a service that keeps track of mobile users as they check in at different locations. This service will get informed of each check-in in real time (a user/location pair) and must be able to answer the following queries in real time:

1. Where is user U right now?
2. What users are at location L right now?

The following requirements apply:

1. A user can only be at one location at a time. If user U checks in at location X and then at location Y, they are no longer at location X.

2. A check-in only valid for at most 2 hours. If user U checks in at location X and then does nothing for 2 hours, they are no longer at location X.

The service should have durable enough storage that you can restart it without losing all of your data It should not store everything in memory.

what kind of DB will you use and how data will be organized and any indexes. If storage is spread out over multiple databases(locations), how is that done?

scalability/availability consideration, how will be distribute multiple servers. what happens when the traffic goes 10x all of sudden. What happens if one of the server goes down.

Design a suggestions list [system design] for words starting with prefix that user has typed on kindle device . The search is based on most frequent item occurring at the top to least frequent item at the bottom. Most frequent item depends on the usage of word globally.

For e.g user types "dra" . There should be a list of suggestions starting with dra such as dragon, drape, dracula etc based on their frequency of usage.

Design a image slide show 1) put image method 2) get image 3) random method. Random method should return a list of images such that images should be in randomized order and no image should be displayed twice without exhausting all images at once. I used list to store images . I used random class to generate randomly generated images based on the interval {0,list.size()}. But he insist on using randomization without depending on the list size.

Given a set of points in a plane, determine the position/angle where a yacht of 30 degree angle could be placed such that it could cover maximum points

Balance a string with parentheses. "a(b)" -> "a(b)"; "(((((" -> ""; "(()())" -> "(()())"; ")ab(()" -> "ab()"; etc...