For each iteration of the string using map, the callback executesindexOf which will iterate over the entire string again. This makes the solution O(n^2). If you know the strings won't ever be that long, then it's fine to optimize for readability. But, if you don't know, at least consider performance.

For each iteration of the string using map, the callback executesindexOf which will iterate over the entire string again. This makes the solution O(n^2). If you know the strings won't ever be that long, then it's fine to optimize for readability. But, if you don't know, at least consider performance.

Yeah, I agree. Whenever I use them, I always comment on what it means. It's a very clever solution and I couldn't have come up with it (I used recursion) but practically unmaintainable.

Could you elaborate on why this is not efficient code ? I do think it is a bit clever as the map function arguments are not explicit enough and you would have to have a deeper understanding of the arguments it takes to know what it all means but it does seem like an efficient solution.