day-six.clj

(require '[clojure.string :as str])
(require '[clojure.set :as set])

(def some-test-data-raw
  ["mjqjpqmgbljsphdztnvjfqwrcgsmlb"
   "bvwbjplbgvbhsrlpgdmjqwftvncz"
   "nppdvjthqldpwncqszvftbrmjlhg"
   "nznrnfrfntjfmvfwmzdfjlvtqnbhcprsg"
   "zcfzfwzzqfrljwzlrfnpqdbhtmscgvjw"])

(def some-expected-first-markers [7 5 6 10 11])

(def real-data-raw (slurp "day-six.txt"))

(defn marker? [data index marker-length]
  ;; just look at the last four characters (including index) and see if they are distinct
  (if (< index (dec marker-length))
    false
    (= marker-length (count (set (subs data (- index (dec marker-length)) (inc index)))))))

(defn solve [data marker-length]
  ;; the inc to go from a zero based index to a character number
  (inc (loop [index 0] (if (marker? data index marker-length) index (recur (inc index))))))

(assert (= (map #(solve % 4) some-test-data-raw) some-expected-first-markers))

(def part-two-test-data-raw ["mjqjpqmgbljsphdztnvjfqwrcgsmlb"
                             "bvwbjplbgvbhsrlpgdmjqwftvncz"
                             "nppdvjthqldpwncqszvftbrmjlhg"
                             "nznrnfrfntjfmvfwmzdfjlvtqnbhcprsg"
                             "zcfzfwzzqfrljwzlrfnpqdbhtmscgvjw"])

(def part-two-expected-markers [19 23 23 29 26])

(assert (= (map #(solve % 14) part-two-test-data-raw) part-two-expected-markers))

;; part one
(solve real-data-raw 4)

;; part two
(solve real-data-raw 14)