Phone Screen

Given logs when people enter and leave
return who was there at each interval

input:

name | start_time | end_time
Abby         10        100
Ben          50        70
Carla        60        90
Bob          110       120

output:

start_time | end_time | names
   10           50       Abby
   50           60       Abby, Ben, Carla
   60           70       Abby, Ben, Carla
   70           90       Abby, Carla
   90           100      Abby
   110          120      Bob

Clarifications:

1. Dont output empty intervals (no people)
2. Multiple people can enter or leave at same time

Coding 1

NxN chess board

N-1 rooks already stay on board so that no one hitting each other. more formally:
no row contains more than 1 rook
no column contains more than 1 rook

place Nth rook, return the position i, j where to place it

but you dont know where current rooks are located

you have a function countRooksInsideRectangle(a,b,c,d) that returns number of rooks within rectangle formed by horizontals a, b (a<=b) and verticals c, d (c<=d)

example
n=3
countRooksInsideRectangle(2,3,1,3) -> 2
countRooksInsideRectangle(1,1,1,1) -> 0
answer: (1,1) (since board is 1-indexed)

Coding 2

chat logs processor

implement two methods
registerEvent(sender, receiver, timestamp)
getMostActiveUser()

activeness is defined as number of chats with other users (at any moment)

i used hashmap<username, hashset>
to keep the active chats for specific user

follow up:
what if we need to return Top K active users
what would we need to change

follow up 2
what if registerEvent is called millions times a day and getMostActiveUser only once a day, what would change

Coding 3

design BookShelfManager class
that has following methods

addBooks(toIndex, books)
removeBooks(fromIndex, toIndex)
moveBooks(fromIndex, toIndex, size)
getBooks()
setBookmarkIndex(index)
getBookmarkIndex()