如何从列表中提取子列表，其中前一个元素的最后一个字符与最后一个元素的第一个字符相同？ - 蟒蛇

Question

The aim of this program is to take a list of words and print the longest possible 'chain' of the words, the conditions of which are that each word has the same first character as the last character of the word before it.

The example I used to test this program is the list of animals:

giraffe
elephant
ant
tiger
raccoon
cat
hedgehog
mouse

The longest chain should read:

hedgehog
giraffe
elephant
tiger
raccoon

However when I run the program below it returns:

giraffe
elephant
tiger
raccoon

Please could someone help to identify the tiny issue with my program that might be causing this. It's probably obvious but I'm fresh out of ideas.

Here is the program:

from random import *


def legal_chain(word, chain):
    """Tests if a word can be 'legally' added to the end
of a chain"""
if word[0] == chain[-1][-1]:
        return True
else: 
    return False

def longest_chain(chain, V, longest):
 """ Returns the longest possible chain of strings where the
 starting character of each string is the same as the last
character from a given starting word and vocabulary V"""

 extended = False
 for word in V:
        if legal_chain(word, chain) is True:
        V.remove(word)
        chain.append(word)
        longest = longest_chain(chain, V, longest)
        extended = True
 if extended is False:
        if len(chain) > len(longest):
        longest = chain

 return longest

def find_longest(chain, V, longest):
    """Finds the longest chain for all possible starting words
   within a given vocabulary V"""
    longs = []
    i = 0
    for word in V:
        chain = [word]
        longer = longest_chain(chain, V, longest)
        longs.append(longer)
    if len(longs) == len(V):
    while len(longs) > 1:
        if len(longs[i]) < len(longs[i + 1]):
            del longs[i]
        elif len(longs[i]) > len(longs[i + 1]):
            del longs[i + 1]
        else:
            i += 1
    return longs

def print_longest(chain, V, longest):
    """Displays the longest chain of words with each word on a new line"""
    the_longest = find_longest(chain, V, longest)
    for list in the_longest:
        for word in list:
            print(word, '\n')




v = open('animals.txt', 'r').readlines()
V = [word.strip() for word in v]
longest = []
chain = []
print_longest(chain, V, longest)

PLEASE IGNORE ANY INDENTATION ERRORS, THE PROGRAM WORKS WITHOUT AN ERROR, THERE IS AN ISSUE WITH COPY AND PASTE!

edit I believe the following fixes the indentation errors (in the sense of no compiler errors, and output is the same as OP had stated):

from random import *


def legal_chain(word, chain):
  """Tests if a word can be 'legally' added to the end of a chain"""
  if word[0] == chain[-1][-1]:
    return True
  else:
    return False

def longest_chain(chain, V, longest):
 """ Returns the longest possible chain of strings where the
 starting character of each string is the same as the last
 character from a given starting word and vocabulary V"""

 extended = False
 for word in V:
    if legal_chain(word, chain) is True:
        V.remove(word)
        chain.append(word)
        longest = longest_chain(chain, V, longest)
        extended = True
    if extended is False:
        if len(chain) > len(longest):
          longest = chain

 return longest

def find_longest(chain, V, longest):
  """Finds the longest chain for all possible starting words
  within a given vocabulary V"""
  longs = []
  i = 0
  for word in V:
    chain = [word]
    longer = longest_chain(chain, V, longest)
    longs.append(longer)
    if len(longs) == len(V):
      while len(longs) > 1:
        if len(longs[i]) < len(longs[i + 1]):
            del longs[i]
        elif len(longs[i]) > len(longs[i + 1]):
          del longs[i + 1]
        else:
                i += 1
  return longs

def print_longest(chain, V, longest):
  """Displays the longest chain of words with each word on a new line"""
  the_longest = find_longest(chain, V, longest)
  for list in the_longest:
    for word in list:
        print(word, '\n')

v = open('animals.txt', 'r').readlines()
V = [word.strip() for word in v]
longest = []
chain = []
print_longest(chain, V, longest)

Answer 1

I think this will help you:

words_array = ['giraffe', 'elephant', 'ant', 'tiger', 'racoon', 'cat', 'hedgedog', 'mouse']

def longest_chain(words_array, current_chain):

    res_chain = list(current_chain)
    test_chain = []

    for s in words_array:
        temp_words_array = list(words_array)
        temp_words_array.remove(s)

        if len(current_chain) == 0:
            test_chain = longest_chain(temp_words_array, current_chain + [s])
        else:
            if s[0] == current_chain[-1][-1]:
                test_chain = longest_chain(temp_words_array, current_chain + [s])

        if len(test_chain) > len(res_chain):
            res_chain = list(test_chain)

    return res_chain


print(longest_chain(words_array, []))

Answer 2

Try this if your list is small:

from itertools import permutations, chain

animals = """giraffe
elephant
ant
tiger
raccoon
cat
hedgehog
mouse"""


longest = sorted([[(j,k) for j, k in zip(i[:-1],i[1:]) if j[-1] == k[0]] \
for i in permutations([i for i in animals.split('\n')])], key=len)[-1]

print list(chain(*[longest[0], [i[1] for i in longest]]))

[out]:

['hedgehog', 'giraffe', 'giraffe', 'elephant', 'tiger', 'raccoon']

NOTE: The list comprehension to get the longest chain is the same as such a nested loop:

animals = animals.split('\n')
animal_chains = []
# Loop through all possible permutations of the list.
for i in permutations(animals): 
    possible_chain = []
    # Reading two items at once in a list.
    for j, k in zip(i[:-1], i[1:]): 
        # Check if last character of the this animal == first character of the next.
        if j[-1] == k[0]:
            possible_chain.append((j,k))
    animal_chains.append(possible_chain)

# sort the animal_chains by length and get the longest.
longest = sorted(animal_chains, key=len)[-1]