solution.cpp

#include <vector>
#include <unordered_map>
#include <string>
#include <iostream>

struct PDU { char header; char c; };
 
std::vector<std::string> reorder(const std::vector<PDU> &pdus) {
    std::unordered_map<int, std::string> words;

    for (auto&& pdu: pdus) {
        const char is_signal = pdu.header & 0x4;

        if (is_signal) {
            continue;
        }

        const int id = (pdu.header & 0xF0) >> 4;

        std::string& w = words[id];

        w.push_back(pdu.c);
    }

    std::vector<std::string> result;
    for (auto&& pair: words) {
        result.push_back(pair.second);
    }

    return result;
}

int main() {
    std::vector<PDU> test{{(char)0xA0, 'A'}, {(char)0xA4, 'L'}, {(char)0xB0, 'O'}, {(char)0xA0, 'L'}, {(char)0xA0, 'A'}};

    auto words = reorder(test);

    for (auto&& w: words) {
        std::cout << w << std::endl;
    }
}