Josephus Problem in Euphoria

Published on 25 February 2023 (Updated: 25 February 2023)

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

Current Solution

include std/io.e
include std/types.e
include std/text.e
include std/get.e as stdget
include std/math.e

-- Indices for value() return value
enum VALUE_ERROR_CODE, VALUE_VALUE, VALUE_NUM_CHARS_READ

-- Indices for parse_int() return value
enum PARSE_INT_VALID, PARSE_INT_VALUE

function parse_int(sequence s)
    -- Trim off whitespace and parse string
    s = trim(s)
    sequence result = stdget:value(s,, GET_LONG_ANSWER)

    -- Error if any errors, value is not an integer, or any leftover characters
    boolean valid = (
        result[VALUE_ERROR_CODE] = GET_SUCCESS
        and integer(result[VALUE_VALUE])
        and result[VALUE_NUM_CHARS_READ] = length(s)
    )

    -- Get value if invalid
    integer value = 0
    if valid
    then
        value = result[VALUE_VALUE]
    end if

    return {valid, value}
end function

procedure usage()
    puts(STDOUT, "Usage: please input the total number of people and number of people to skip.\n")
    abort(0)
end procedure

-- 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(integer n, integer k)
    integer g = 0
    for m = 2 to n
    do
        g = mod(g + k, m)
    end for

    return g + 1
end function

-- Check 1st and 2nd command-line argument
sequence argv = command_line()
if length(argv) < 5 or length(argv[4]) = 0 or length(argv[5]) = 0
then
    usage()
end if

-- Parse 1st and second command-line argument
sequence arg_nums = {4, 5}
sequence values = {}
for m = 1 to 2
do
    sequence result = parse_int(argv[arg_nums[m]])
    values &= result[PARSE_INT_VALUE]
    if not result[PARSE_INT_VALID]
    then
        usage()
    end if
end for

-- Calculate Josephus problem and display
integer n = values[1]
integer k = values[2]
integer g = josephus(n, k)
printf(STDOUT, "%d\n", g)

Josephus Problem in Euphoria was written by:

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.