If you did the exercise duplicate you already have a function named has_duplicates that takes a list as a parameter and returns True if there is any object that appears more than once in the list.
Use a set to write a faster, simpler version of has_duplicates.
Answer
Checking the membership of an element in a set (line 4) is very fast (constant time) compared to checking the membership in a list (linear time). This is why this implementation should be preferred to the one given in a .
def has_duplicates(elements):
visited = set()
for i in range(len(elements)):
if elements[i] in visited:
return True
else:
visited.add(elements[i])
return False
Exercise 2: rotate-pairs
Two words are "rotate pairs" if you can rotate one of them and get the other (see ). Write a program that reads a wordlist and finds all the rotate pairs.
Answer
For convenience, we provide the implementation of rotate_word, that rotates a word by a given shift.
from string import ascii_lowercase
def rotate_word(word, shift):
rotated = ''
for letter in word.lower():
index = ascii_lowercase.find(letter)
index = (index + shift) % len(ascii_lowercase)
rotated += ascii_lowercase[index]
return rotated
def find_rotate_pairs(words_list):
words_set = {word.strip().lower() for word in words_list}
rotate_pairs = []
for word in words_set:
for shift in range(1, len(ascii_lowercase)):
rotated = rotate_word(word, shift)
if rotated in words_set:
rotate_pairs.append((word, rotated, shift))
return rotate_pairs
Although there is an overhead for transforming the list of words into a set (line 10), for large list it improve considerably the performance when checking the membership of the rotated word (line18).