JavaScript Coding Challenge #10

Ever heard of CodeFights? If you didn’t, you must sign up now! It’s a lot of fun, I promise! :D

I’ve played some time and last week and I ended up on top 1. ^_^

CodeFights is a website where you can test your coding skills against friends, co-workers and company bots. And the best part is that they have support for a lot of programming languages, including JavaScript. Yey!

It’s great if you want to prepare yourself for an interview because they have a lot of interview problems.

Today we’re going to take a look at one of them which is called: the Line Encoding problem:

Given a string, return its encoding defined as follows:

First, the string is divided into the least possible number of disjoint substrings consisting of identical characters, for example, "aabbbc" is divided into ["aa", "bbb", "c"].

Next, each substring with length greater than one is replaced with a concatenation of its length and the repeating character, for example, substring "bbb" is replaced by "3b".

Finally, all the new strings are concatenated together in the same order and a new string is returned.

Example

For s = "aabbbc", the output should be lineEncoding(s) = "2a3bc".

To be honest, it took me a while until I figured it out, but it was a lot of fun! I recommend you do the same before you continue to read this. It will help you a lot on the long run if you struggle with it instead of just jumping to the end.

My approach is a bit different then what they suggest in the problem, but it does the trick. :D

First we need to loop through all the letters of the string and compare each pair of two consecutive letters:

function lineEncoding(s) {
    
    for(var i=0; i < s.length; i++){
        if(s[i] === s[i+1]){
        }
    }
}

We’re going to add a count x which will hold the number of identical consecutive letters, and also a variable result in which we’re going to save the final output of your program:

function lineEncoding(s) {
    var x = 1;    
    var result = '';
    for(var i=0; i < s.length; i++){
        if(s[i] === s[i+1]){
        }
    }
    return result;
}

We initialize x with 1 and increment it by 1 every time the next letter is identical.

function lineEncoding(s) {
    var x = 1;    
    var result = '';
    for(var i=0; i < s.length; i++){
        if(s[i] === s[i+1]){
            x += 1;
        }
    }
    return result;
}

Now we’re going to store a concatenation of x with the current letter s[i] everytime the next letter s[i+1] is different. We also need to reset x:

function lineEncoding(s) {
    var x = 1;    
    var result = '';
    for(var i=0; i < s.length; i++){
        if(s[i] === s[i+1]){
            x += 1;
        } else {
            result += x+s[i];
            x = 1;
        }
    }
    return result;
}

Great! Now let’s test it:

lineEncoding('aabbbc'); // 2a3b1c
lineEncoding('aabbbcccc'); // 2a3b4c

Hmmm… It works almost well… but the problem is that we print 1 also. The problem says that we can only print the length of the substring which is bigger than one.

This little issue can be solved easily with the string’s replace function:

function lineEncoding(s) {
    var x = 1;    
    var result = '';
    for(var i=0; i < s.length; i++){
        if(s[i] === s[i+1]){
            x += 1;
        } else {
            result += x+s[i];
            x = 1;
        }
    }
    return result.replace(/1/g, '');
}

We’re passing a regular expression /1/g which matches every occurrence of the character 1 and replace it with an empty string ''.

Conclusion

Do you have a better solution for this problem? Please don’t hesitate to let me know about it in the comments sections bellow. I’ve learned a lot from people who submitted their own solutions on the previous coding challenges. Find out more about them here.

I hope you enjoyed this and I would sincerely appreciate a click on the Recommend button 💚.

Happy coding! ^_^