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Twitter_240305.cpp
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Twitter_240305.cpp
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// れおまる(@reomaru_1103)さん作の問題の解答
// https://twitter.com/dc1394/status/1764844324624466075
#include <cstdint> // for std::int32_t
#include <iostream> // for std::cout, std::endl
#include <optional> // for std::optional
#include <string> // for std::string, std::to_string
namespace {
static auto constexpr N = 10000;
static auto constexpr M = 999;
std::optional<std::int32_t> get_answer();
} // namespace
int main()
{
if (auto const answer = get_answer()) {
std::cout << "answer = " << *answer << std::endl;
}
return 0;
}
namespace {
std::optional<std::int32_t> get_answer()
{
auto cnt = 1;
for (auto i = 1; i < N; i++) {
auto const str = std::to_string(i);
auto const chk = str.find("4");
auto const chk2 = str.find("9");
if (chk != std::string::npos || chk2 != std::string::npos) {
continue;
}
if (cnt == M) {
return std::make_optional(i);
}
cnt++;
}
return std::nullopt;
}
} // namespace