# Competitive coding problem

I want to print a series like
0 0 | 10 0 | 10 20 | -20 20 | -20 -20 | 30 -20 | 30 40 | -40 40 | -40 -40 | 50 -40 | …

Well, short of giving you the answer, try to figure out what it is doing. First of all, I’d think of this as two problems: the left number and the right number. Assuming we’re doing this with a `for` loop, how does each number relate to the index? Assuming you are starting at something like `i = 0`, how do you derive each number sequence from that. You are going to have a use a few little math tricks to do it - see if you can figure it out. If it helps, ignore the `0`s at the end of the numbers - they are trivial.

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Hi @ajinkyabawaskar, welcome on the forum.
Here is a tip: notice that you modify alternately the first and the second number of the couple. In none of the elements in the list, both numbers are modified at the same time. Also notice that the signs of the numbers are alternated and they follow a specific pattern. As @kevinSmith said, focusing on each number singularly helps to understand such pattern.

Also, can you provide us with the code that you tried to so far? You can use codepen.io or JSFiddle

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I know codepen isn’t meant for C code, but I am using it anyways as I haven’t discovered any C fiddles yet. Also, I know the code I shared has poor coding practices like no proper naming of variables and maybe it just sucks. I was supposed to solve this problem in half an hour without an IDE, if I did, I’d have been eligible to appear for an interview for a job that pays 18k\$/year. I am not able to do anything, not getting the solution is bugging me, even though I have traced the pattern, I am not able to convert it to code even though I know it is just loops and conditionals. Sorry about the details. Here’s what I achieved so far - https://codepen.io/xajinkya/pen/jgabym - the first digit in pattern without minus sign

repl.it will let you create a C environment (they support many different languages)

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Thank you @ieahleen

Hi @ajinkyabawaskar , I’d like to say few things.

First, I do hope this question has not been asked on the forum during those 30 minutes you mentioned because the idea behind these questions are to evaluate the candidate, not his/her network.

Secondly, you should mark as the solution one of the posts of the people that provided an answer to the question, not your own answer where you added the link to the online code.
If the idea was that to make it stick at the start of the page, you can edit your own post to provide the additional information.