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May 11, 2017 01:10
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Improved breadth first product
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| defmodule BreadthFirst do | |
| defp init_cursor(dimension) do (for _ <- 1..dimension, do: 0) end | |
| defp increment_cursor(cursor, depth, max, carry) do | |
| cursor | |
| |>List.foldr( | |
| {carry, false, []}, | |
| fn elem, {carry, unique, acc} -> | |
| case elem + carry do | |
| ^depth -> {1, unique, [0 | acc]} | |
| ^max -> {0, true , [max | acc]} | |
| sum -> {0, unique, [sum | acc]} | |
| end | |
| end) | |
| end | |
| defp next_cursor(acc, cursor, depth, max, carry) do | |
| case increment_cursor(cursor, depth, max, carry) do | |
| {1, _unique, _cursor} -> | |
| acc # carry out, so we have hit the max depth | |
| {_carry, true, cursor} -> | |
| next_cursor([cursor | acc], cursor, depth, max, 1) | |
| {_carry, false, cursor} -> | |
| next_cursor(acc, cursor, depth, max, max) # not unique, seen in lower depth | |
| end | |
| end | |
| defp product_at_depth(dimension, 1) do [init_cursor(dimension)] end | |
| defp product_at_depth(dimension, depth) do | |
| max = depth-1 # the max value | |
| next_cursor([], init_cursor(dimension), depth, max, max) | |
| |> Enum.reverse | |
| end | |
| def product(dimension, depth) when dimension >= 1 and depth >= 1 do | |
| for i <- 1..depth do product_at_depth(dimension, i) end | |
| end | |
| end |
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