(Python 3.5)

Purpose: To practice recursion on a more interesting problem

For this problem, you will be given a pokemon evolution book as a dictionary. The keys to this dictionary are pokemon names, and the value for each key is a list of pokemon that can be evolved into. The following is a sample of what this dictionary might look like:

book1 = { "squirtle" : ["wartortle"], "wartortle" : ["blastoise"], "blastoise" : [], "charmander" : ["charmeleon"], "charmeleon" : ["charizard"], "charizard" : [], "bulbasaur" : ["ivysaur"], "ivysaur" : ["venusaur"], "venusaur" : [] } book2 = { "eevee" : ["jolteon", "flareon", "vaporeon"], "jolteon" : ["zapdos"], "vaporeon" : ["articuno"], "flareon" : ["moltres"] } book3 = { 'cubone': ['dragonite', 'magmar', 'tangela'], 'krabby': ['vaporeon', 'chansey', 'zapdos', 'electabuzz'], 'spearow': ['mewtwo', 'seadra', 'tentacool'], 'primeape': ['weepinbell', 'hitmonchan', 'mew', 'porygon', 'dewgong'], 'snorlax': ['moltres', 'dragonair', 'dratini', 'mewtwo', 'mew'], 'wartortle': ['rattata', 'weepinbell', 'seaking'], 'flareon': ['porygon', 'dratini', 'articuno'], 'clefairy': ['staryu'], 'rattata': ['bellsprout', 'nidorino'], 'machoke': ['staryu', 'bellsprout'], 'vileplume': ['doduo', 'victreebel', 'machop', 'starmie', 'kabuto'], 'dugtrio': ['golem', 'kadabra', 'rapidash', 'hitmonchan', 'aerodactyl'], 'venusaur': [], 'bulbasaur': [], 'onix': ['horsea'], 'weezing': ['snorlax'], 'beedrill': ['grimer', 'bellsprout', 'clefable', 'arbok'], 'butterfree': ['persian', 'dragonair', 'machop', 'starmie', 'dodrio'], 'charmeleon': ['oddish', 'seel', 'persian', 'seaking', 'poliwrath'], 'paras': ['seadra'], 'raticate': ['raichu', 'voltorb', 'sandshrew'], 'gyarados': ['articuno', 'moltres', 'flareon', 'dratini'], 'mr.mime': [], 'kabutops': ['dragonite', 'aerodactyl', 'mewtwo', 'dragonair'], 'poliwhirl': ['golem', 'graveler', 'magikarp', 'electabuzz', 'mr.mime'], 'muk': ['tauros', 'omanyte', 'mewtwo', 'electrode', 'cubone'], 'rapidash': ['gyarados', 'electrode'], 'golem': [], 'rhydon': ['jynx'], 'zapdos': ['dragonair', 'mewtwo', 'dratini'], 'golduck': ['hypno', 'dewgong', 'jolteon', 'poliwag'], 'gengar': ['jolteon', 'seaking', 'jynx'], 'arcanine': [], 'mew': [], 'gloom': [], 'vulpix': ['wigglytuff'], 'articuno': ['mew', 'zapdos', 'dragonair'], 'ponyta': ['eevee', 'tauros', 'mr.mime', 'horsea'], 'pinsir': ['ditto', 'zapdos'], 'grimer': ['kabutops'], 'nidoqueen': [], 'tangela': ['horsea', 'scyther', 'pinsir', 'kabutops', 'mewtwo'], 'ivysaur': ['marowak', 'krabby', 'growlithe'], 'electabuzz': ['gyarados', 'ditto', 'kabutops', 'porygon'], 'weedle': ['raichu', 'mew', 'snorlax', 'voltorb'], 'omanyte': ['mewtwo', 'zapdos'], 'magnemite': [], 'marowak': ['dratini', 'porygon', 'kabutops', 'goldeen'], 'pidgey': [], 'dragonair': [], 'poliwag': [], 'magikarp': ['articuno', 'kabutops', 'lapras', 'mew'], 'fearow': ['omastar'], 'slowpoke': ['koffing', 'farfetchd', 'hypno', 'krabby', 'gengar'], 'starmie': ['dragonite', 'magikarp', 'scyther'], 'ekans': ['slowbro', 'paras', 'electrode', 'rapidash'], 'meowth': ['dodrio', 'poliwrath', 'ditto', 'tentacool', 'aerodactyl'], 'raichu': [], 'kabuto': ['aerodactyl', 'articuno', 'kabutops'], 'charizard': [], 'oddish': ['flareon', 'horsea', 'drowzee', 'tauros'], 'wigglytuff': ['dragonite', 'oddish'], 'pidgeot': ['seel', 'bellsprout'], 'hitmonlee': ['seaking', 'mew', 'gyarados'], 'charmander': [], 'mewtwo': ['mew'], 'bellsprout': ['tauros', 'gengar', 'electabuzz', 'ponyta'], 'hypno': ['flareon'], 'kadabra': [], 'nidoking': ['venonat', 'muk', 'farfetchd', 'zubat', 'articuno'], 'sandslash': ['gyarados', 'golbat', 'alakazam', 'mewtwo', 'poliwrath'], 'diglett': ['graveler'], 'ditto': ['kabuto', 'vaporeon', 'aerodactyl'], 'arbok': ['horsea', 'primeape', 'hitmonlee'], 'abra': ['grimer', 'tangela', 'dragonite'], 'jigglypuff': [], 'tentacool': ['weezing', 'mewtwo', 'farfetchd', 'moltres', 'grimer'], 'tentacruel': ['dodrio'], 'tauros': ['flareon', 'moltres', 'porygon', 'omanyte'], 'dodrio': [], 'exeggcute': [], 'victreebel': ['tentacruel', 'seaking', 'ditto', 'lapras'], 'nidoranfemale': ['jynx', 'persian', 'shellder', 'mewtwo'], 'shellder': ['vaporeon', 'marowak', 'articuno', 'tauros', 'gyarados'], 'nidorino': ['omanyte', 'gastly', 'magneton', 'marowak', 'paras'], 'aerodactyl': ['zapdos'], 'kingler': ['mew', 'cubone', 'mr.mime', 'dratini', 'weezing'], 'seadra': ['mr.mime', 'scyther', 'jynx', 'electabuzz', 'magmar'], 'exeggutor': ['mr.mime', 'dragonite', 'hitmonchan', 'flareon', 'gyarados'], 'koffing': ['weezing', 'chansey', 'omastar'], 'farfetchd': ['rhyhorn', 'cloyster', 'moltres', 'vaporeon', 'dodrio'], 'jolteon': ['kabutops', 'snorlax', 'omastar', 'aerodactyl'], 'sandshrew': ['lickitung', 'nidoranmale', 'clefairy'], 'magmar': ['snorlax', 'tauros', 'pinsir', 'lapras'], 'electrode': ['lapras', 'staryu', 'seaking', 'marowak', 'horsea'], 'dratini': [], 'mankey': ['farfetchd', 'electrode'], 'magneton': ['mr.mime', 'kabutops'], 'staryu': ['ditto', 'dratini'], 'seaking': ['staryu', 'magikarp', 'starmie', 'dragonite'], 'caterpie': ['weedle', 'vulpix', 'shellder', 'moltres'], 'blastoise': ['electrode', 'vileplume', 'gastly', 'goldeen', 'sandslash'], 'pidgeotto': ['lickitung', 'spearow'], 'pikachu': ['hitmonlee'], 'weepinbell': [], 'gastly': ['seadra', 'mew', 'rhydon', 'horsea', 'tangela'], 'scyther': ['jynx', 'articuno', 'mew'], 'porygon': ['aerodactyl', 'mewtwo', 'kabuto'], 'poliwrath': ['machop', 'victreebel', 'seel', 'gengar', 'vaporeon'], 'dragonite': ['mewtwo', 'mew'], 'geodude': ['magneton', 'seel', 'cubone'], 'hitmonchan': [], 'lickitung': [], 'eevee': ['articuno', 'jolteon', 'flareon'], 'venomoth': [], 'moltres': ['dragonair'], 'metapod': [], 'horsea': ['moltres'], 'graveler': ['seaking', 'tangela', 'slowpoke'], 'kangaskhan': ['dragonite', 'kabuto', 'zapdos', 'moltres'], 'cloyster': ['mr.mime', 'marowak', 'kabutops', 'gengar', 'eevee'], 'machop': ['staryu', 'machamp', 'slowpoke', 'dodrio'], 'kakuna': ['scyther', 'zubat'], 'voltorb': ['porygon', 'pinsir', 'dragonite', 'jolteon', 'moltres'], 'ninetales': ['farfetchd', 'parasect', 'ponyta', 'mewtwo'], 'machamp': ['onix', 'marowak'], 'jynx': ['dratini', 'tauros', 'snorlax'], 'seel': ['haunter', 'kangaskhan'], 'dewgong': ['hitmonchan', 'pinsir', 'eevee'], 'growlithe': ['kabutops', 'shellder', 'farfetchd', 'chansey'], 'vaporeon': ['porygon', 'jolteon', 'aerodactyl'], 'haunter': ['koffing', 'rhyhorn', 'aerodactyl'], 'nidorina': [], 'alakazam': ['krabby', 'machoke', 'tauros', 'horsea'], 'venonat': ['magmar', 'drowzee'], 'nidoranmale': [], 'omastar': [], 'golbat': ['scyther', 'parasect', 'oddish'], 'parasect': ['persian', 'electabuzz'], 'squirtle': [], 'drowzee': [], 'chansey': ['pinsir', 'vaporeon'], 'slowbro': [], 'rhyhorn': ['staryu'], 'clefable': ['golbat', 'ditto'], 'goldeen': ['magikarp'], 'zubat': ['eevee', 'gyarados', 'dodrio', 'seadra'], 'doduo': ['shellder'], 'lapras': ['omanyte', 'omastar', 'mewtwo'], 'persian': ['golduck'], 'psyduck': ['abra'], } 

In the example above, squirtle can (eventually) evolve into a blastoise by first evolving into a wartortle, but never into an eevee. On the other hand, eevee can evolve into any one of flareon, jolteon or vaporeon. Note that a pokemon that can no longer evolve might be in the book and associated with an empty list (like blastoise above) or might not be in the book at all. Either case is fine and your program needs to handle both cases correctly.

You are guaranteed, however, that the pokemon book will be structured such that a pokemon cannot "devolve". Thus, if pokemon A can, either directly or indirectly, evolve into pokemon B, then it will not be possible for B to evolve back into A.

Your task is to write a recursive function that will answer the question of whether a source pokemon can eventually evolve into a given target pokemon. Your function should have 3 parameters: the source, the target and the pokemon dictionary to use to check for possible evolutions. Your function should return True if it is possible for source to become the target and False otherwise.

Your function should be no longer than 12 lines of code (not counting comments) and possibly less (ours is 8). If you find your solution is getting any longer than that, you are overthinking it!

Sample Run:

We are providing you with 3 sample pokemon books to use; you can just copy/paste the dictionary literals into your code :

print("Using book1, can bulbasaur evolve to venusaur?") print(can_evolve(book1, "bulbasaur", "venusaur")) print("Using book1, can charmeleon evolve to blastoise?") print(can_evolve(book1, "charmeleon", "blastoise")) print("Using book2, can eevee evolve to articuno?") print(can_evolve(book2, "eevee", "articuno")) print("Using book3, can cubone evolve to charizard?") print(can_evolve(book3, "cubone", "charizard")) print("Using book3, can magikarp evolve to mewtwo?") print(can_evolve(book3, "magikarp", "mewtwo")) 

If you test your program with the sample code provided, you should get ouput that looks like this:

Using book1 , can bulbasaur evolve to venusaur ? True

Using book1 , can charmeleon evolve to blastoise ? False

Using book2 , can eevee evolve to articuno ? True

Using book3 , can cubone evolve to charizard ? False

Using book3 , can magikarp evolve to mewtwo ? True

Part 2: Analysis

In the problem description above, we gave you a guarantee about the structure of the pokemon book: that it was not possible for a pokemon to "devolve". What if you DIDNT have this guarantee? Write a short paragraph (2-to-4 sentences is enough) describing the problem(s) this would cause for your program and how you might possibly attempt to address these problems

(python 3.5)