exercism/elisp/anagram/anagram.el

;;; anagram.el --- Anagram (exercism)

;;; Commentary:

;;; Code:

(provide 'anagram)

(defun get-char-count (w)
  "Return an associative list of character counts for W."
  (let ((char-list (string-to-list w))
        (char-count ()))
    ;; Build an associative list from the character list.
    (dolist (char char-list char-count)
      (let ((entry (assoc char char-count)))
        (if entry (cl-incf (cdr entry))
          (push (cons char 1) char-count))))))

(defun equal-char-count (char-count comparison-char-count)
  "Return t if the submitted character counts are equal, false otherwise.
CHAR-COUNT and COMPARISON-CHAR-COUNT should be alists in (character . count) format."
  (let ((are-equal t))
    (dolist (char-count char-count are-equal)
      (if (not are-equal) nil)
      (if (assoc (car char-count) comparison-char-count)
          (if (not (equal
                    (cdr char-count)
                    (cdr (assoc (car char-count) comparison-char-count))))
              (setq are-equal nil))
        (setq are-equal nil)))))

(defun anagrams-for (word anagrams)
  "Return all elements of ANAGRAMS which are anagrams for WORD.
Case insensitive."
  (let ((candidates ())
        (word-char-count (get-char-count (downcase word))))
    (dolist (candidate anagrams candidates)
      (when (and (not (string-equal word candidate))
                 (= (length word) (length candidate))
                 (equal-char-count word-char-count (get-char-count (downcase candidate))))
        (push candidate candidates)))
    (reverse candidates)))

;;; anagram.el ends here