Is there std algorithm or their combination to find the longest sequences of repeating values in a sorted array?

Functional specification

In a sorted array (or vector) find the longest sequences of repeated values. The size of array is expected to be relatively large (up to a million of entries).

Please see the fully functional demo.

Reservation

Just to avoid the first optimization suggestion: actual code uses my implementation of Incremental upper bound in sorted range instead of std::upper_bound; just don't want to overcomplicate things here.

Question

Is there a way to express this in terms of C++ Standard Library algorithms using one (or a simple combination) of them to make this code more generic and avoid reinventing the wheel?

I really don’t like this code because of two loops with two passes and the ugly if-else-if, but I don’t see a way to improve it easily.

I still hope some std algorithm or their combination could do this work much simpler.

The code

#include <algorithm>#include <iostream>#include <vector>std::pair<std::vector<size_t>,size_t> get_longest_ranges(auto first, auto last){    ptrdiff_t max_range = 0;    size_t amount_of_ranges = 0;    auto it = first;    while (it != last) {        auto it_end = std::upper_bound(it, last, *it);        if (max_range == it_end - it) {++amount_of_ranges;        } else if (max_range < it_end - it) {            max_range = it_end - it;            amount_of_ranges = 1;        }        it = it_end;    }    std::vector<size_t> ranges;    ranges.reserve(amount_of_ranges);    it = first;    while (it != last) {        auto it_end = std::upper_bound(it, last, *it);        if (it_end - it == max_range) {            ranges.push_back(it-first);        }        it = it_end;    }    return { ranges,  max_range };}int main() {    std::vector<int> v = { 1, 1, 1, 2, 2, 2, 2, 3, 3, 4, 4, 5, 6, 6, 6, 7, 7, 7, 7 };    auto [starts, length] = get_longest_ranges(v.begin(),v.end());    std::cout << "Max equal elements range length = " << length;    for (auto start : starts) {        std::cout << "\nAt position: " << start << " Values: ";        for (size_t i = start; i < start + length; i++) {            std::cout << v[i] << " ";        }    }}

The expected result

For the code above the expected result is:

Max equal elements range length = 4
At position: 3 Values: 2 2 2 2
At position: 15 Values: 7 7 7 7