Erik Rantapaa erantapaa

This is a quick tutorial on how to use the set-cover package to solve exact cover problems.

Exact Cover Problems

Given a set X and collection of subsets of X, S, the exact cover problem asks if there is a sub-collection S' of S s.t. the subsets in S' are pairwise disjoint and their union equals X.

My quick summary of Python 2.7 strings and Unicode.

Overview

Python has two string types:

type str
type unicode

Examples:

	{-# LANGUAGE FlexibleContexts #-}

	--- Some experiments vis-a-vis the Gale-Shapely algorithm.

	import Data.List
	import Control.Monad
	import Data.Array
	import Data.Array.MArray
	import Data.Array.ST
	import Data.Ord

	#
	# Simple BibTeX file parsing in python.
	#
	# See `bibtest1` for an example of usage.
	#
	# This is a good overview of how to correctly parse a bibtex file:
	#
	# http://maverick.inria.fr/~Xavier.Decoret/resources/xdkbibtex/bibtex_summary.html

	import string

	module Lib
	where

	import Control.Monad
	import Control.Monad.Primitive
	import Control.Monad.ST
	import qualified Data.Vector.Unboxed.Mutable as UVM
	import qualified Data.Vector.Unboxed as UV

	calculate_codes :: PrimMonad m => UV.Vector Int -> UV.Vector Int -> m (UV.Vector Int)

	L-systems in Haskell.
	===

	> import Data.List.Split (splitOn)
	> import Data.List
	>
	> type Rules = [(Char, String)]
	>
	> -- compute the next generation
	> next :: Rules -> String -> String

	{-# LANGUAGE Rank2Types #-}
	{-# LANGUAGE FlexibleContexts #-}

	import Data.Reflection
	import Data.Proxy

	data M a s = M a -- Note the phantom comes after the concrete

	-- In `normalize` we're tying the knot to get the phantom types to align
	-- note that reflect :: Reifies s a => forall proxy. proxy s -> a

	Emulating an Enigma machine
	===

	In this gist I'll go over the development of an Enigma machine encoder
	in Haskell.

	Here are some useful background info about how the Enigma machine works:

	- Enigma Simulator: http://enigmaco.de/enigma/enigma.html
	- "How Enigma Machines Work" http://enigma.louisedade.co.uk/howitworks.html

	<html>
	<body>

	<script>

	function toChar(ch) {
	return (ch == '' ? ' ' : ch)
	}

	function next(grid) {


	// Solution for [2015-09-11] Challenge #231 [Hard] Eight Husbands for Eight Sisters
	//
	// https://www.reddit.com/r/dailyprogrammer/comments/3kj1v9/20150911_challenge_231_hard_eight_husbands_for/
	//
	// NOTE: This is ugly Java - lots of global variables, etc.

	import java.util.Arrays;
	import java.util.ArrayList;
	import java.util.List;