Question

For example:

<1,2,3> as an input to the function comb to get combination of 2 elements will output result <<1,2>,<1,3>,<2,3>>, which as input to same function will get
<<<1,2>,<1,3>>,<<1,3>,<2,3>>,<<1,2>,<2,3>>, which as input to the same function will get
….

Logic is the same, only type changes, so it can be made generic.
I tried to write something like this:

template<typename V>
vector<vector<vector<V>::const_iterator>> comb(const vector<V>){
   ....

   while(next_combination(...))
   vector<vector<vector<V>::const_iterator>> results;
   return results;
}

vector<string> input
comb(comb(comb(input)));

But compiler keep complaining can’t deduce the returning value’s type.

Thanks.

Answer 1

Maybe the following will help:

template <typename T>
vector<vector<T> > comb(vector<T> v)
{
    vector<vector<T> > result;
    // may want to sort the input vector before iterating over the combinations
    do {
        result.push_back(v);
    } while (next_combination(...));
    return result;
}

Note the changes:

• The return value of comb is a vector of vectors
• The parameter of comb is not const because next_combination changes it
• There is much copying of vectors inside comb; all that copying seems necessary