Josephus Problem in Rust

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

Current Solution

use std::env::args;
use std::process::exit;
use std::str::FromStr;

fn usage() -> ! {
    println!("Usage: please input the total number of people and number of people to skip.");
    exit(0);
}

fn parse_int<T: FromStr>(s: &str) -> Result<T, <T as FromStr>::Err> {
    s.trim().parse::<T>()
}

// Reference: https://en.wikipedia.org/wiki/Josephus_problem#The_general_case
//
// Use zero-based index algorithm:
//
//    g(1, k) = 0
//    g(m, k) = [g(m - 1, k) + k] MOD m, for m = 2, 3, ..., n
//
// Final answer is g(n, k) + 1 to get back to one-based index
fn josephus(n: i32, k: i32) -> i32 {
    let mut g: i32 = 0;
    for m in 2..=n {
        g = (g + k) % m;
    }

    g + 1
}

fn main() {
    let mut args = args().skip(1);

    // Exit if 1st command-line argument not an integer
    let mut n: i32 = args
        .next()
        .and_then(|s| parse_int(&s).ok())
        .unwrap_or_else(|| usage());

    // Exit if 2nd command-line argument not an integer
    let mut k: i32 = args
        .next()
        .and_then(|s| parse_int(&s).ok())
        .unwrap_or_else(|| usage());

    // Run Josephus problem and store results
    println!("{}", josephus(n, k));
}

Josephus Problem in Rust was written by:

• rzuckerm

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

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