Sorting with comparator


Sort with comparator
A vector (like an array)  can be sorted using the sort() function. But this function sorts in ascending order by default. To sort an array in a different order, you need to use the so-called comparator  - a function that sets the sort order by comparing two objects.
 
Example
An example of a comparator that sorts the elements of an array in ascending order. bool cmp(int first, int second) { return first < second; }
and sorting the vector A using the created comparator: sort(A.begin(), A.end(), cmp); Think about iterators

Training problem

Vector sort: Start

According to the condition of the problem, it is clear that it is necessary to apply stable (stable) sorting, therefore, instead of sort, stable_sort should be used.

Training problem

Sort by sum of digits

you can also specify a function object as a comparator, which you can create before calling the sort function.
For example:
struct {
        bool operator()(int a, int b) const
        {
            return a < b;
        }
    }cmp;

Training problem

Sorting a vector through a function object