Create ranges from an array of integers

Given an array of ints, return a string identifying the range of
numbers.


Example:

• Input arr - [0 1 2 7 21 22 1098 1099]

• Output - "0-2,7,21-22,1098-1099"

Is there any improvement possible in this implementation?

#include
#include
#include
#include

std::string  range_creator(std::vector & vec)
{
    std::sort(std::begin(vec),std::end(vec));

    int first=vec.at(0);
    int prev=first-1;

    std::stringbuf buffer;
    std::ostream os (&buffer);

    for(auto &x : vec)
    {
       if(++prev == x)
           continue;
        else
        {

           if(first != --prev)
           {               
               os  vec={0,1,2,7,8,9,10,21,22,23,24,25,27,1098,1099,1100,2000};
    std::cout<<range_creator(vec);

    return 0;
}

You can make good use of std::adjacent_find. Like this:

std::string range_creator(std::vector & vec)
{
    auto first = std::begin(vec), last = std::end(vec);
    if(first == last)
        return "";
    std::sort(first, last);
    std::stringbuf buffer;
    std::ostream os (&buffer);
    while(true)
    {
        auto mid = std::adjacent_find(first, last,
                [](int x, int y){ return x + 1 != y; });
        if(mid == last)
            break;
        if(first == mid)
            os << *first << ",";
        else
            os << *first << "-" << *mid << ",";
        first = ++mid;
    }
    if(first == --last)
        os << *first;
    else
        os << *first << "-" << *last;
    return buffer.str();
}

I think my code is still subject to further improvements, but I'm no expert, so I'll leave it to the community.

StackExchange Code Review Q#85552, answer score: 4