Отсортировать числа по возрастанию суммы составляющих цифр

task156.cpp

#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
 
using std::cout;
using std::vector;
 
template <typename ContainerT, bool stable = false>
class digsum_sort
{
	using ValueType = typename ContainerT::value_type;
	using IteratorType = typename ContainerT::iterator;
	using ComparatorType = std::function<bool(ValueType, ValueType)>;
	using SortFuncType = std::function<void(IteratorType, IteratorType, ComparatorType)>;
public:
	digsum_sort()
	{
		cmp_func = [](ValueType a, ValueType b)
		{
			std::div_t div;
			int sum_a = 0, sum_b = 0;
			for (div.quot = a; div.quot > 0; sum_a += div.rem) { div = std::div(div.quot, 10); }
			for (div.quot = b; div.quot > 0; sum_b += div.rem) { div = std::div(div.quot, 10); }
			return sum_a < sum_b;
		};
 
		sort_func = stable
			? std::stable_sort<IteratorType, ComparatorType>
			: std::sort<IteratorType, ComparatorType>;
	}
 
	void operator()(ContainerT &arr)
	{
		sort_func(std::begin(arr), std::end(arr), cmp_func);
	}
 
private:
	ComparatorType cmp_func;
	SortFuncType sort_func;
};
 
void show_array(const vector<int> &arr)
{
	cout << "{ ";
	for (int a : arr) {
		cout << a << " ";
	}
	cout << "}\n";
}
 
int main()
{
	vector<int> arr;
 
	arr = { 19, 22, 30 };
	show_array(arr);
	digsum_sort<vector<int>, false>()(arr);
	cout << "-->\n";
	show_array(arr);
 
	cout << "\n";
 
	arr = { 25, 123, 6000, 11111, 77, 30, 999, 1000000 };
	show_array(arr);
	digsum_sort<vector<int>, true>()(arr);
	cout << "-->\n";
	show_array(arr);
 
	return 0;
}