Дмитрий

#include <string>
#include <string_view>
#include <ranges>
#include <array>
#include <utility>
#include <algorithm>
#include <cassert>
#include <stdexcept>

template <typename Key, typename Value, std::size_t Size>
struct Map {
	std::array<std::pair<Key, Value>, Size> data;

	constexpr Value at(const Key key) const {
		const auto iter = std::find_if(std::begin(data), std::end(data),
			[&key](const auto& v) { return v.first == key; });

		if (iter == std::end(data)) {
			throw std::range_error("unknown character");
		}
		return iter->second;
	}
};

static constexpr std::array<std::pair<std::string_view, char>, 51> MORSE_MAP = { {
	{"•-", 'A'},      {"-•••", 'B'},    {"-•-•", 'C'},   {"-••", 'D'},
	{"•", 'E'},       {"••-•", 'F'},    {"--•", 'G'},    {"••••", 'H'},
	{"••", 'I'},      {"•---", 'J'},    {"-•-", 'K'},    {"•-••", 'L'},
	{"--", 'M'},      {"-•", 'N'},      {"---", 'O'},    {"•--•", 'P'},
	{"--•-", 'Q'},    {"•-•", 'R'},     {"•••", 'S'},    {"-", 'T'},
	{"••-", 'U'},     {"•••-", 'V'},    {"•--", 'W'},    {"-••-", 'X'},
	{"-•--", 'Y'},    {"--••", 'Z'},    {"-----", '0'},  {"•----", '1'},
	{"••---", '2'},   {"•••--", '3'},   {"••••-", '4'},  {"•••••", '5'},
	{"-••••", '6'},   {"--•••", '7'},   {"---••", '8'},  {"----•", '9'},
	{"•-•-•-", '.'},  {"--••---", ','}, {"---•••", ':'}, {"••--••", '?'},
	{"•----•", '\''}, {"-••••-", '-'},  {"-••-•", '/'},  {"-•--•", '('},
	{"-•--•-", ')'},  {"•-••-•", '"'},  {"-•••-", '='},  {"•-•-•", '+'},
	{"-••-", 'x'},    {"•--•-•", '@'},  {"/", ' '} } };

constexpr auto decode(std::string_view morse) {
	constexpr auto map = Map<std::string_view, char, MORSE_MAP.size()>{ MORSE_MAP };
	return morse
		| std::ranges::views::split(' ')
		| std::ranges::views::transform([](auto&& range) {
			return map.at(std::string_view{ range });
		})
		| std::ranges::to<std::string>();
}

int main() {
	const auto CODE = "•••• • •-•• •-•• --- --••--- / •-- --- •-• •-•• -••";
	const auto TEXT = "HELLO, WORLD";

	assert(decode(CODE) == TEXT);

	return 0;
}