42 lines
1.2 KiB
Common Lisp
42 lines
1.2 KiB
Common Lisp
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;;; anagram.lisp
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;;; 2018-01-31
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;;;
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;;; Lisp implementation of this tweet:
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;;; https://twitter.com/fermatslibrary/status/958700402647674880.
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;;;
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;;; Fun fact: this uses the prime list generated by
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;;; (prime-numbers 26 3)
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;;; using prime.rkt in the par/ toplevel directory. Why start at 3? It
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;;; was a typo.
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(defpackage #:anagram
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(:use #:cl)
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(:export #:anagram-p))
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(in-package #:anagram)
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(defun deconstruct (w)
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"Convert a string into a list of characters (instead of an array of
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characters)."
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(loop for c across w collect c))
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(defparameter *mapping*
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(pairlis
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(deconstruct "abcdefghijklmnopqrstuvwxyz")
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'(3 5 7 11 13 17 19 23 29 31 37 41 43 47
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53 59 61 67 71 73 79 83 89 97 101 103)))
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(defun lookup (c)
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"A hack to convert a character to its relevant prime."
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(cdr (assoc c *mapping*)))
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(defun word-number (word)
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"Convert a word to a number by multiplying the associated prime
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number for all the letters in the word."
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(apply #'* (mapcar #'lookup
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(deconstruct (string-downcase word)))))
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(defun anagram-p (&rest words)
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"Given a list of words, return T if they are all anagrams of each
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other."
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(apply #'= (mapcar #'word-number words)))
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