52.py

"""Problem 52: Write a function nearly_equal to test whether two strings are nearly equal. Two strings a and
b are nearly equal when a can be generated by a single mutation on b."""

import string


def insert_char(input_string, character, pos):
    return input_string[:pos] + character + input_string[pos:]


def replace_char(input_string, character, pos):
    return input_string[:pos] + character + input_string[pos + 1:]


def swap_chars(input_string, pos1, pos2):
    return replace_char(replace_char(input_string, input_string[pos1], pos2), input_string[pos2], pos1)


def mutate(input_string):
    result = {}  # define the result as a set: unordered collection of unique values
    alphabet = string.ascii_lowercase  # all lowercase letters of the alphabet

    result = {
        replace_char(input_string, '', s[0]) for s in enumerate(input_string)
    }  # all mutations of input_string with 1 char removed

    result = result.union(
        {insert_char(input_string, letter, i) for i in range(len(input_string) + 1) for letter in alphabet}
    )  # all mutations of input string with 1 char inserted

    result = result.union(
        {replace_char(input_string, letter, s[0]) for s in enumerate(input_string) for letter in alphabet}
    )  # all mutations of input string with 1 char replaced

    result = result.union(
        {swap_chars(input_string, i, i + 1) for i in range(len(input_string) - 1)}
    )  # all mutations of input string with consecutive chars swapped

    return result


def nearly_equal(string1, string2):
    return string1 in mutate(string2)


print(nearly_equal('python', 'perl'))
print(nearly_equal('perl', 'pearl'))
print(nearly_equal('python', 'jython'))
print(nearly_equal('man', 'woman'))