# a good example why tech companies test leetcode style questions.

Today I came across a question that is simple enough for most developers to solve fast, but just slightly complex enough to worth a little bit of discussion. I believe this questions, and my answer to it, is a pretty good demonstration why leetcode style interview exists. Let's look at the problem first:
https://leetcode.com/problems/isomorphic-strings/

The real problem at hand is how do you confirm whether two strings are representationally the same. Representationally, sorry for the unclear diction, because you can transform the strings into a representations of the order of appearance and how many of different kinds in each word.

so essentially, a good way to show an isomorphic representation of a string would be like:
egg = 122
therefore egg and add are isomorphic

isomorphic = 1234356718;

``````var isIsomorphic = function(s, t) {
if (!s || !t) return false;
if(s.length !== t.length) return false;

let sMap = {};
let tMap = {};
let sNumString = '';
let tNumString = '';
let currentS = '';
let currentT = ''
for (let i=0; i<s.length; i++) {
currentS = s[i];
currentT = t[i];

if(!sMap[currentS]) {
sMap[currentS] = Object.keys(sMap).length + 1
}
else {
sNumString += sMap[currentS]
}

if(!tMap[currentT]) {
tMap[currentT] = Object.keys(tMap).length + 1
}
else {
tNumString += tMap[currentT]
}
}

return sNumString === tNumString
};

``````

I think questions like one this really digs deep into whether a developer really knows and is skillful at general problem solving and would be an indicator whether the employee will be good for the company.

(Although I don't know if my solution to this would be well-received at interviews when it is usually not possible to test the validity of code.)

I really dislike problems that are very esoteric and dependent on contextual knowledge. For example, you'd need to know a specific formula for solving how many prime numbers are in [0 ... n]. This type of problem is just terrible and not worthwhile to learn.

Another reason why I like the isomorphic string problem so much, because not only it is knowledge independent, but also does not require a huge mental aerobatic like https://leetcode.com/problems/maximum-subarray/
I would say, however, questions like maximum-subarray do show whether a candidate has reach a higher level of computational, emphasis here, solving skill. Except that in interviews, it's hugely frustrating if you haven't seen a problem remotely similar beforehand.

Do you have a similar question in mind that is like this one ? Please comment and let me know!