Josephus Problem in Php

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

Current Solution

<?php
function usage()
{
    exit("Usage: please input the total number of people and number of people to skip.");
}

function parse_int($str_value)
{
    // Remove leading and trailing spaces
    $str_value = trim($str_value);

    // Make sure all digits
    if (preg_match("/^[+-]?\d+$/", $str_value) === FALSE)
    {
        return FALSE;
    }

    // Make sure valid integer
    if (
        filter_var(
            $str_value,
            FILTER_VALIDATE_INT,
            array(
                'options' => array(
                    'decimal' => TRUE,
                    'min_range' => PHP_INT_MIN,
                    'max_range' => PHP_INT_MAX
                )
            )
        ) === FALSE
    )
    {
        return FALSE;
    }

    return intval($str_value);
}

// 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
function josephus($n, $k)
{
    $g = 0;
    for ($m = 2; $m <= $n; $m++)
    {
        $g = ($g + $k) % $m;
    }

    return $g + 1;
}

// Exit if too few arguments
if (count($argv) < 3)
{
    usage();
}

// Parse arguments. Exit if invalid
$n = parse_int($argv[1]);
$k = parse_int($argv[2]);
if ($n === FALSE || $k === FALSE)
{
    usage();
}

// Run Josephus problem and store results
$g = josephus($n, $k);
echo "${g}\n";

Josephus Problem in Php 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.