Question

For a little something I was trying out in C++, I have accepted a string (say ‘a tomato is red’) and gotten rid of spaces (‘atomatoisred’).

Now how would I go about deleting recurring characters only, on condition that the first instance of that character gets to stay (so our example becomes,’atomisred’)?

Thanks in advance!

Answer 1

You can use the erase-remove idiom in conjunction with a set keeping track of the duplicate characters:

std::set<char> dupes;

str.erase(
    std::remove_if(
        str.begin(), str.end(),
        [&](char c) { return not dupes.insert(c).second; }),
    str.end());

This also uses the fact that the return value of std::set::insert is a pair whose second element is a bool indicating whether the insertion took place.