# Basic math required for interviews?

I've had different interviewers going too deep into Mathy parts of CS.

Design your own hash table, was able to breeze thru most parts. Then got stuck at generating a good hash function, avoiding collisions and taking into account the position of each character input. I didn't remember the specific Mathy part of this.

Given a tree that is always complete, I represented the tree as an array and jump to any node on the tree by knowing the number of nodes for each level. I forgot the algebra equation to count these nodes from n to m via levels. It was a strange tree structure.

If a candidate was able to get that far and just didn't remember an implementation detail. Is it acceptable and could just wave your hand to these small things or do you ding them for it? The interviewer wasn't impressed and expected me to know all these Mathy portions. Even when I have the best space and runtime.

I usually wave my hand pass these little things because they don't show how good of a programmer you are. These are Google-able items. What you think?

• Apple Azrael3
I can accept the hash function part, as you can do a PhD on hash functions alone.
Not being able to derive a tree mapping is indefensible IMO. Just shows poor interview prep.
Oct 15 3
• Northrop Grumman / Eng sad-panda
OP
The tree wasn't a normal binary tree.
Oct 15
• Apple Azrael3
The point of the interview was then to see if you can derive from basics, and the question served it’s purpose I’d say.
Oct 15
• Northrop Grumman / Eng sad-panda
OP
So forgetting this equation caused me to fail?
https://en.wikipedia.org/wiki/Summation
Oct 15
• Wayfair zDkt58
I think those things matter, especially your hash example.
Oct 15 2
• Northrop Grumman / Eng sad-panda
OP
But tbh, do you ever implement your own hash function and need to know exactly the math part? Knowing internally how it works is enough.
Oct 15
• Wayfair zDkt58
If i was asked to then I’d expect to know it. Sure I haven’t implemented it in a long time but it’s a very strong assumption to say those sorts of skills are never needed. They show an attention to detail and a general inclination to consider the intricacies of what technology you’re using.
Oct 15