Question 1 was #1570, dot product of two sparse vectors. Interviewer did not allow me to start coding until I mentioned different data structures that could be used to solve this to his satisfaction. I mentioned 3 and then he asked the downsides of solving the problem with each data structure I had mentioned:

• HashMap - I said hash function may or may not be constant
• Array pairs - I sad array pairs could end up using more space than the HashMap
• LinkedList - I said unlike the array, LL would ont allow random access and it would use more memory

He insisted I wasn't listing disadvantages, then he noticed we'd been discussing this for 18 minutes and let me begin writing code. He picked the data structure out from the options I had given; I wrote the code that solved the problem without issue!

The second question was a variation of #56, Merge Intervals which I had not seen before but I'm confident I solved it but we ran out of time to discuss it.

Question: What disadvantages of data structures was he insisting on for #1570? Because I asked him what advice he would give me for the interview process and he said to study data structures; but I don't know what disadvantages he was thinking of and I haven't been able to come up with a better answer