Вы можете использовать:
template <typename IT>
std::size_t count_repetition(IT begin, IT end, std::size_t count)
{
std::size_t res = 0;
auto it = begin;
while (it != end) {
it = std::adjacent_find(it, end);
if (it == end){
return res;
}
const auto it2 = std::find_if(it, end, [it](const auto& e) { return e != *it; });
const auto dist = std::distance(it, it2);
if (count <= dist) {
// how to count 2-repetition for {a, a, a, a}
#if 0
++res; // Count only as 1
#else
res += dist + 1 - count; // count as 3
#endif
}
it = it2;
}
return res;
}
Демо