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Mutable data structures
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lib/examples/josephus.ex
defmodule InPlace.Examples.Josephus do
@moduledoc """
https://en.wikipedia.org/wiki/Josephus_problem
"""
alias InPlace.LinkedList
@doc """
Form the circle from N soldiers.
Going clockwise, eliminate every k-th soldier
until only one soldier is left.
"""
def solve(num_soldiers, every_k) do
circle = LinkedList.new(num_soldiers)
Enum.each(1..num_soldiers, fn n -> LinkedList.append(circle, n) end)
_number_of_moves =
LinkedList.iterate(
circle,
fn p, acc ->
if rem(acc, every_k) == 0 do
LinkedList.delete_pointer(circle, p)
end
acc + 1
end,
initial_value: 1,
stop_on: fn _ -> LinkedList.size(circle) == 1 end
)
## the survivor
LinkedList.data(circle, LinkedList.head(circle))
end
end