Josephus Problem in C++

Josephus

Problem in C++

Welcome to the Josephus Problem in C++ page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

#include <charconv>
#include <iostream>
#include <optional>
#include <string_view>

[[noreturn]] void usage() {
    std::cerr << "Usage: please input the total number of people and number of "
                 "people to skip.\n";
    std::exit(1);
}

static constexpr std::string_view ws = " \t\n\r\f\v";
constexpr std::string_view trim(std::string_view s) {
    const auto start = s.find_first_not_of(ws);
    if (start == std::string_view::npos) return "";
    s.remove_prefix(start);

    const auto end = s.find_last_not_of(ws);
    s.remove_suffix(s.size() - 1 - end);
    return s;
}

std::optional<int> to_nonnegative_int(std::string_view s) {
    int value{};
    auto [ptr, ec] = std::from_chars(s.data(), s.data() + s.size(), value);
    return (ec == std::errc{} && ptr == s.data() + s.size() && value > 0)
               ? std::make_optional(value)
               : std::nullopt;
}

int josephus(int n, int k) {
    int survivor = 0;
    for (int i = 1; i <= n; ++i) {
        survivor = (survivor + k) % i;
    }
    return survivor + 1;
}

int main(int argc, char* argv[]) {
    if (argc != 3) usage();

    const auto n = to_nonnegative_int(argv[1]);
    const auto k = to_nonnegative_int(argv[2]);

    if (!n || !k) usage();

    std::cout << josephus(*n, *k) << '\n';
}

Josephus Problem in C++ was written by:

• Apurva Vats
• Ștefan-Iulian Alecu

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

No 'How to Implement the Solution' section available. Please consider contributing.

How to Run the Solution

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