#include <iostream>
#include <numeric>
#include <map>
using namespace std;
int main()
{
    const std::map<uint32_t,uint32_t> m = { {1,5}, {100,400}, {10,40}};

    auto irq_count = [](std::map<uint32_t, uint32_t> irq_map) {
        uint32_t max_irq_num
            = std::accumulate(irq_map.cbegin(), irq_map.cend(),
                              uint32_t(0) /* starting max value */,
                              [](uint32_t curr_max, auto irq_iter) {
                                  return std::max(curr_max, irq_iter.first);
                              });
        return max_irq_num;
    };
    auto irq_count2 = [](std::map<uint32_t, uint32_t> irq_map) {
        uint32_t max_irq_num = 0;
        for (const auto iter : irq_map)
        {
            max_irq_num = std::max(max_irq_num, iter.first);
        }
        return max_irq_num;
    };

    auto irq_count3 = [](const std::map<uint32_t, uint32_t>& irq_map) {
        return std::max_element(irq_map.begin(), irq_map.end(), [](const auto& lhs, const auto& rhs) { return lhs.first < rhs.first;})->first;
    };

    auto irq_count4 = [] (const auto& irq_map)
    {
        // Relies on irq_map being ordered map, constructed with the default comperator
        return irq_map.rbegin()->first;
    };

    cout << irq_count(m) << endl;
    cout << irq_count2(m) << endl;
    cout << irq_count3(m) << endl;
    cout << irq_count4(m) << endl;
}