Background: 3 YOE, came from a no-name college.
Position: SDE II
Location: SF HQ
Date: June 2020

This was all conducted over google hangouts

Round 1 (Coding)

Given a square matrix of size NxN, complete the latin square. 
A Latin square is a square that contains N sets of numbers from 1 to N arranged tthat no such row or column contains the same number twice.

[1, x, 3, 4]       [1, 2, 3, 4]
[x, 1, 4, 3]  ->   [3, 4, 1, 2]
[3, 4, x ,x]       [4, 3, 2, 1]
[4, 3, 2, 1]       [2, 1, 4 ,3]

Round 2 (Engineering Manager)
Talked about my resume, asked me some behavioral questions regarding goals, and why I am interested in postmates.

Round 3 (Coding)
Two coding questions

Question 1
Given an array of time window, [startTime, endTime, capacity]. which represents all the couriers. Output the timeslots with its corresponding capacities.

Input
[0, 2, 10], [2, 3, 5], [10, 12, 3], [1,7, 10], [2,9, 1] 

Output
{timeSlot: Capacity}
{0: 21}
{1: 21}
{2: 26}
{3: 15}
......

Question 2
Given a starting number and ending number and an array of numbers. Return true or false if we can add/substract/multiple/divide to the starting number that will result in the ending number. The numbers can not be used twice.

Start = 0, End = 10 nums [1, 2, 4, 9]  

1 + 9 = 10 
return True

Round 4
Design whatsapp using a PULL based model only.
Key features:
-one-one conversation
-user discovery based on phone number
-delivered/read recipt
-MMS support
-group chats

He put a constraint on this saying that users can only pull from server which meant that no push model will be used.