Algorithm for joining e.g. an array of strings

Question

I have wondered for some time, what a nice, clean solution for joining an array of strings might look like. Example: I have ["Alpha", "Beta", "Gamma"] and want to join the strings into one, separated by commas – "Alpha, Beta, Gamma". Now I know that most programming languages offer some kind of join method for this. I just wonder how these might be implemented. When I took introductory courses, I often tried to go it alone, but never found a satisfactory algorithm. Everything seemed rather messy, the problem being that you can not just loop through the array, concatenating the strings, as you would add one too many commas (either before or after the last string). I don’t want to check conditions in the loop. I don’t really want to add the first or the last string before/after the loop (I guess this is maybe the best way?). Can someone show me an elegant solution? Or tell me exactly why there can’t be anything more elegant?

Accepted Answer

The most elegant solution i found for problems like this is something like this (in pseudocode)

```
separator = ""
foreach(item in stringCollection)
{
    concatenatedString += separator + item
    separator = ","
}
```

You just run the loop and only after the second time around the separator is set. So the first time it won't get added. It's not as clean as I'd like it to be so I'd still add comments but it's better than an if statement or adding the first or last item outside the loop.

Algorithm for joining e.g. an array of strings

Solution

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