Implement autocorrect, which takes a user_word, a list of all valid_words, a diff_function, and a limit. If the user_word is contained inside the valid_words list, autocorrect returns that word. Otherwise, autocorrect returns the word from valid_words that has the lowest difference from the provided user_word based on the diff_function. However, if the lowest difference between user_word and any of the valid_words is greater than limit, then user_word is returned instead.
A diff function takes in three arguments, which are the two strings to be compared (first the user_word and then a word from valid_words), as well as the limit. The output of the diff function, which is a number, represents the amount of difference between the two strings.
Assume that user_word and all elements of valid_words are lowercase and have no punctuation.
Important: if multiple strings have the same lowest difference according to the diff_function, autocorrect should return the string that appears first in valid_words.