
Data structures and algorithms interview questions and their solutions - abhimt
https://techiedelight.quora.com/500-Data-Structures-and-Algorithms-practice-problems-and-their-solutions?__filter__&__nsrc__=2&__snid3__=1594232728&amp;share=1
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hanoz
Didn't most of us get in to this mathsy line of work precisely because we
didn't need to memorise a load of stuff and could just work things out from
first principles as and when required?

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burkaman
I don't like coding interviews, but this list is for practice, not
memorization. Ideally you could solve all of these from first principles.

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munin
If this isn't a metaphor for the programming interview I don't know what is:
[http://www.techiedelight.com/multiply-two-numbers-without-
us...](http://www.techiedelight.com/multiply-two-numbers-without-using-
multiplication-operator-loops/)

"Implement multiplication without using loops."

"Uh, okay. What do you mean by loops?"

"Don't use a conditional loop."

"What do you mean by a conditional loop?"

"Oh, you know, the standard definition."

Time passes.

"I'm stuck. What is the answer?"

"Oh, you just have a loop on b dividing it by 2 using shift operators until it
is zero."

"Wait a minute, you said you couldn't use loops."

"Did I? Ah, well."

Hackerrank/leetcode exercises are written the same way. So many times that a
problem asks "Output the indexes of two numbers in the array such that their
sum is K" and you write your code and the website says "INCORRECT! You said
[3,6] but the right answer was [6,3]". Addition is commutative! The two are
equal! And both right!

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userbinator
The real way to multiply without loops is to use a lookup table, or unroll the
(fixed iteration) shift-and-add loop.

That page is both hilarious and sad at the same time. Hilarious because the
second "solution" clearly has a loop, and sad because sites like those don't
really help anyone. Some of the pages on that site are downright _WTF_ s:

[http://www.techiedelight.com/generate-binary-
numbers-1-n/](http://www.techiedelight.com/generate-binary-numbers-1-n/)

~~~
bogomipz
>"or unroll the (fixed iteration) shift-and-add loop"

Can you elaborate on this? I understand the shifting but didn't understand the
"loop unrolling fixed iteration part"

~~~
userbinator
The shift-and-add algorithm for multiplication is usually implemented as a
loop that iterates for the number of bits of the operand, so e.g. for an 8-bit
x 8-bit multiplication, the loop runs 8 times. (An "early out" algorithm when
one of the operands becomes 0 is also common, but let's not complicate things
here.) It's trivial to unroll this loop into the 8 individual shift-and-add
steps.

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sp527
Most interview questions are ridiculous and don’t test for the knowledge a
candidate should have. When I interview, I ask a system design problem that
involves using an inverted index, a bst, understanding how to normalize data,
and then being a little clever when merging some data. It tests fundamental
concepts in the context of building a working solution to a meaningful
problem.

I never understood why anyone would ask say DP questions in an interview. We
don’t use that in 99.9% of software (I’ve never once in my career found a use
case). What you’re really testing is whether or not the candidate had enough
time to refresh that material. Worse still, it involves a very rigid solution
pattern that’s over-specified to that class of problem and tells you nothing
about what you want to know: can a candidate synthesize concepts to devise a
solution to problems we actually encounter?

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ccleary00
I'd rather just not interview at companies that have these kinds of interviews
and save myself the hassle.

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pmoriarty
Sadly, the code examples all seem to be in C++ ... not exactly the ideal
language for pedagogy.

~~~
quickben
They have stuff like bit manipulations and the likes, C++ makes sense for
those.

~~~
nonis
Doesn't virtually every programming language have operators for bit
manipulation?

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manigandham
If anyone asks these questions without a particular scenario to actually deal
with in the course of the position you're interviewing for, you are in for
some bullshit at that company. This has become all too common at the major
corporations sadly.

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bloaf
Am I stupid or do both of the solutions to the problem

"Replace each element of array with product of every other element without
using / operator"

use the / operator?

My solution would involve summing the log() of the values in the array.

~~~
NiceGuy_Ty
There was just a post on HN to a site that went over this exact problem.
Essentially, you do two linear scans to calculate the product of every number
before an index, and to calculate the product of every number after an index.
Then, for each index, the answer is just multiplying those two numbers you
found for that index.

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tgarma1234
That's a great list worthy of study in any context.

~~~
jhasbro
I agree. I studied these sorts of questions through hackerrank, leetcode, etc.
and became a better programmer. That said, I wouldn’t want to work somewhere
where they asked me to find a “zero sum sub array” in an interview

