--- /dev/null
+{
+ "cells": [
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "# Word chains\n",
+ "\n",
+ "\"Word chain\" puzzles are where you transform one word into another, by changing one letter at a time, with all the intermediate steps being valid words. \n",
+ "\n",
+ "For instance, you can transform 'rash' to 'jags' like this:\n",
+ "\n",
+ "```\n",
+ "rash\n",
+ "Bash\n",
+ "basS\n",
+ "baGs\n",
+ "Jags\n",
+ "```\n",
+ "\n",
+ "(the capital letter is the one changed in each step).\n",
+ "\n",
+ "## Part 1\n",
+ "\n",
+ "Given this [list of words](words4.txt), what is the minimum number of steps to go from `vice` to `wars`?"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 1,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "import string\n",
+ "import heapq"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 2,
+ "metadata": {},
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "2336"
+ ]
+ },
+ "execution_count": 2,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "words = [w.strip() for w in open('words4.txt').readlines()]\n",
+ "len(words)"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 3,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "def adjacents(word):\n",
+ " return [word[0:i] + l + word[i+1:]\n",
+ " for i in range(len(word))\n",
+ " for l in string.ascii_lowercase\n",
+ " if l != word[i]]"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 4,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "neighbours = {w: [n for n in adjacents(w) if n in words]\n",
+ " for w in words}"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 5,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "def distance(w1, w2):\n",
+ " return sum(1 for i in range(len(w1))\n",
+ " if w1[i] != w2[i])"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 6,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "# def extend(chain):\n",
+ "# return [chain + [s] for s in neighbours[chain[-1]]\n",
+ "# if s not in chain]"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 7,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "def extend(chain, closed=None):\n",
+ " if closed:\n",
+ " nbrs = set(neighbours[chain[-1]]) - closed\n",
+ " else:\n",
+ " nbrs = neighbours[chain[-1]]\n",
+ " return [chain + [s] for s in nbrs\n",
+ " if s not in chain]"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 8,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "def extend_raw(chain):\n",
+ " nbrs = [w for w in adjacents(chain[-1]) if w in words]\n",
+ " return [chain + [s] for s in nbrs\n",
+ " if s not in chain]"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 9,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "def bfs_search(start, goal, debug=False):\n",
+ " agenda = [[start]]\n",
+ " finished = False\n",
+ " while not finished and agenda:\n",
+ " current = agenda[0]\n",
+ " if debug:\n",
+ " print(current)\n",
+ " if current[-1] == goal:\n",
+ " finished = True\n",
+ " else:\n",
+ " successors = extend(current)\n",
+ " agenda = agenda[1:] + successors\n",
+ " if agenda:\n",
+ " return current\n",
+ " else:\n",
+ " return None "
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 19,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "def bfs_search_closed(start, goal, debug=False):\n",
+ " agenda = [[start]]\n",
+ " closed = set()\n",
+ " finished = False\n",
+ " while not finished and agenda:\n",
+ " current = agenda[0]\n",
+ " if debug:\n",
+ " print(current)\n",
+ " if current[-1] == goal:\n",
+ " finished = True\n",
+ " else:\n",
+ " closed.add(current[-1])\n",
+ " successors = extend(current, closed)\n",
+ " agenda = agenda[1:] + successors\n",
+ " if agenda:\n",
+ " return current\n",
+ " else:\n",
+ " return None "
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 10,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "def dfs_search(start, goal, debug=False):\n",
+ " agenda = [[start]]\n",
+ " finished = False\n",
+ " while not finished and agenda:\n",
+ " current = agenda[0]\n",
+ " if debug:\n",
+ " print(current)\n",
+ " if current[-1] == goal:\n",
+ " finished = True\n",
+ " else:\n",
+ " successors = extend(current)\n",
+ " agenda = successors + agenda[1:]\n",
+ " if agenda:\n",
+ " return current\n",
+ " else:\n",
+ " return None "
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 11,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "def astar_search(start, goal, debug=False):\n",
+ " agenda = [(distance(start, goal), [start])]\n",
+ " heapq.heapify(agenda)\n",
+ " finished = False\n",
+ " while not finished and agenda:\n",
+ " _, current = heapq.heappop(agenda)\n",
+ " if debug:\n",
+ " print(current)\n",
+ " if current[-1] == goal:\n",
+ " finished = True\n",
+ " else:\n",
+ " successors = extend(current)\n",
+ " for s in successors:\n",
+ " heapq.heappush(agenda, (len(current) + distance(s[-1], goal) - 1, s))\n",
+ " if agenda:\n",
+ " return current\n",
+ " else:\n",
+ " return None "
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 12,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "# Uses direct lookup of successors, rather than using cached neighbours in the dict\n",
+ "def astar_search_raw(start, goal, debug=False):\n",
+ " agenda = [(distance(start, goal), [start])]\n",
+ " heapq.heapify(agenda)\n",
+ " finished = False\n",
+ " while not finished and agenda:\n",
+ " _, current = heapq.heappop(agenda)\n",
+ " if debug:\n",
+ " print(current)\n",
+ " if current[-1] == goal:\n",
+ " finished = True\n",
+ " else:\n",
+ " successors = extend_raw(current) # Difference here\n",
+ " for s in successors:\n",
+ " heapq.heappush(agenda, (len(current) + distance(s[-1], goal) - 1, s))\n",
+ " if agenda:\n",
+ " return current\n",
+ " else:\n",
+ " return None "
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 13,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "def astar_search_closed(start, goal, debug=False):\n",
+ " agenda = [(distance(start, goal), [start])]\n",
+ " heapq.heapify(agenda)\n",
+ " closed = set()\n",
+ " finished = False\n",
+ " while not finished and agenda:\n",
+ " _, current = heapq.heappop(agenda)\n",
+ " if debug:\n",
+ " print(current)\n",
+ " if current[-1] == goal:\n",
+ " finished = True\n",
+ " else:\n",
+ " closed.add(current[-1])\n",
+ " successors = extend(current, closed)\n",
+ " for s in successors:\n",
+ " heapq.heappush(agenda, (len(current) + distance(s[-1], goal) - 1, s))\n",
+ " if agenda:\n",
+ " return current\n",
+ " else:\n",
+ " return None "
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 14,
+ "metadata": {},
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "['vice', 'dice', 'dire', 'dare', 'ware', 'wars']"
+ ]
+ },
+ "execution_count": 14,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "astar_search('vice', 'wars')"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 15,
+ "metadata": {},
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "['vice', 'dice', 'dire', 'dare', 'ware', 'wars']"
+ ]
+ },
+ "execution_count": 15,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "astar_search_raw('vice', 'wars')"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 16,
+ "metadata": {},
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "6"
+ ]
+ },
+ "execution_count": 16,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "len(astar_search('vice', 'wars'))"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 17,
+ "metadata": {},
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "6"
+ ]
+ },
+ "execution_count": 17,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "len(bfs_search('vice', 'wars'))"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 20,
+ "metadata": {},
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "6"
+ ]
+ },
+ "execution_count": 20,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "len(bfs_search_closed('vice', 'wars'))"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 21,
+ "metadata": {},
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "793"
+ ]
+ },
+ "execution_count": 21,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "len(dfs_search('vice', 'wars'))"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 22,
+ "metadata": {},
+ "outputs": [
+ {
+ "name": "stdout",
+ "output_type": "stream",
+ "text": [
+ "10000 loops, best of 3: 158 µs per loop\n"
+ ]
+ }
+ ],
+ "source": [
+ "%%timeit\n",
+ "astar_search('vice', 'wars')"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 23,
+ "metadata": {},
+ "outputs": [
+ {
+ "name": "stdout",
+ "output_type": "stream",
+ "text": [
+ "100 loops, best of 3: 15.6 ms per loop\n"
+ ]
+ }
+ ],
+ "source": [
+ "%%timeit\n",
+ "astar_search_raw('vice', 'wars')"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 24,
+ "metadata": {},
+ "outputs": [
+ {
+ "name": "stdout",
+ "output_type": "stream",
+ "text": [
+ "10000 loops, best of 3: 168 µs per loop\n"
+ ]
+ }
+ ],
+ "source": [
+ "%%timeit\n",
+ "astar_search_closed('vice', 'wars')"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 25,
+ "metadata": {},
+ "outputs": [
+ {
+ "name": "stdout",
+ "output_type": "stream",
+ "text": [
+ "1 loop, best of 3: 1min 40s per loop\n"
+ ]
+ }
+ ],
+ "source": [
+ "%%timeit\n",
+ "bfs_search('vice', 'wars')"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 26,
+ "metadata": {},
+ "outputs": [
+ {
+ "name": "stdout",
+ "output_type": "stream",
+ "text": [
+ "1 loop, best of 3: 597 ms per loop\n"
+ ]
+ }
+ ],
+ "source": [
+ "%%timeit\n",
+ "bfs_search_closed('vice', 'wars')"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 27,
+ "metadata": {},
+ "outputs": [
+ {
+ "name": "stdout",
+ "output_type": "stream",
+ "text": [
+ "10 loops, best of 3: 85.5 ms per loop\n"
+ ]
+ }
+ ],
+ "source": [
+ "%%timeit\n",
+ "dfs_search('vice', 'wars')"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "## Part 2\n",
+ "\n",
+ "The example shows that `jags` is reachable in four steps from `rash`. There are 11 words one step away from `rash`: \n",
+ "`bash`, `cash`, `dash`, `gash`, `hash`, `lash`, `mash`, `rasp`, `rush`, `sash`, and `wash`. \n",
+ "\n",
+ "There are 47 words reachable in one or two steps from `rash`. They are `base`, `bash`, `bask`, `bass`, `bast`, `bath`, `bosh`, `bush`, `case`, `cash`, `cask`, `cast`, `dash`, `dish`, `gash`, `gasp`, `gosh`, `gush`, `hash`, `hasp`, `hath`, `hush`, `lash`, `lass`, `last`, `lath`, `lush`, `mash`, `mask`, `mass`, `mast`, `math`, `mesh`, `mush`, `push`, `ramp`, `rasp`, `ruse`, `rush`, `rusk`, `rust`, `sash`, `sass`, `tush`, `wash`, `wasp`, and `wish`.\n",
+ "\n",
+ "There are 180 words reachable in up to three steps from `rash`.\n",
+ "\n",
+ "How many words are reachable in up to ten steps from `vice`?"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 28,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "def reachable_in(word, n, trim_extras=False):\n",
+ " reachable = set()\n",
+ " boundary = set([word])\n",
+ " for i in range(n):\n",
+ " extras = set()\n",
+ " for w in boundary:\n",
+ " extras.update(neighbours[w])\n",
+ " if trim_extras:\n",
+ " extras.difference_update(reachable)\n",
+ " reachable.update(boundary)\n",
+ " boundary = extras.copy()\n",
+ " return reachable.union(extras).difference(set([word]))"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 29,
+ "metadata": {
+ "scrolled": true
+ },
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "(11,\n",
+ " '`bash`, `cash`, `dash`, `gash`, `hash`, `lash`, `mash`, `rasp`, `rush`, `sash`, `wash`')"
+ ]
+ },
+ "execution_count": 29,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "len(reachable_in('rash', 1)), ', '.join(sorted('`{}`'.format(r) for r in reachable_in('rash', 1)))"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 30,
+ "metadata": {
+ "scrolled": true
+ },
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "(47,\n",
+ " '`base`, `bash`, `bask`, `bass`, `bast`, `bath`, `bosh`, `bush`, `case`, `cash`, `cask`, `cast`, `dash`, `dish`, `gash`, `gasp`, `gosh`, `gush`, `hash`, `hasp`, `hath`, `hush`, `lash`, `lass`, `last`, `lath`, `lush`, `mash`, `mask`, `mass`, `mast`, `math`, `mesh`, `mush`, `push`, `ramp`, `rasp`, `ruse`, `rush`, `rusk`, `rust`, `sash`, `sass`, `tush`, `wash`, `wasp`, `wish`')"
+ ]
+ },
+ "execution_count": 30,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "len(reachable_in('rash', 2)), ', '.join(sorted('`{}`'.format(r) for r in reachable_in('rash', 2)))"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 31,
+ "metadata": {
+ "scrolled": true
+ },
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "180"
+ ]
+ },
+ "execution_count": 31,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "len(reachable_in('rash', 3))"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 32,
+ "metadata": {
+ "scrolled": true
+ },
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "2195"
+ ]
+ },
+ "execution_count": 32,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "len(reachable_in('rash', 10))"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 33,
+ "metadata": {
+ "scrolled": true
+ },
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "2192"
+ ]
+ },
+ "execution_count": 33,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "len(reachable_in('vice', 10))"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 34,
+ "metadata": {
+ "scrolled": true
+ },
+ "outputs": [
+ {
+ "name": "stdout",
+ "output_type": "stream",
+ "text": [
+ "100 loops, best of 3: 5.82 ms per loop\n"
+ ]
+ }
+ ],
+ "source": [
+ "%%timeit\n",
+ "len(reachable_in('rash', 10))"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 35,
+ "metadata": {
+ "scrolled": true
+ },
+ "outputs": [
+ {
+ "name": "stdout",
+ "output_type": "stream",
+ "text": [
+ "100 loops, best of 3: 2.75 ms per loop\n"
+ ]
+ }
+ ],
+ "source": [
+ "%%timeit\n",
+ "len(reachable_in('rash', 10, trim_extras=True))"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": null,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": []
+ }
+ ],
+ "metadata": {
+ "kernelspec": {
+ "display_name": "Python 3",
+ "language": "python",
+ "name": "python3"
+ },
+ "language_info": {
+ "codemirror_mode": {
+ "name": "ipython",
+ "version": 3
+ },
+ "file_extension": ".py",
+ "mimetype": "text/x-python",
+ "name": "python",
+ "nbconvert_exporter": "python",
+ "pygments_lexer": "ipython3",
+ "version": "3.5.2+"
+ }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}
projects / ou-summer-of-code-2017.git / blobdiff