clojure light table demo code

union.clj

;; code from Austin Clojure Meetup light table live coding
;; implement union alogrithm from Sedgewick/Wayne class
;; -- https://class.coursera.org/algs4partI-2012-001/
;; lecture notes week 1 - https://d19vezwu8eufl6.cloudfront.net/algs4partI/slides%2F15UnionFind.pdf

;; every state has a unique group id
(def no-connections 
  [0 1 2 3 4 5 6 7 8 9])

;; two states are connected if they have the 
;; same group id
(defn connected? [state i j]
  (= (nth state i)
     (nth state j)))

;; if the two states have different group ids,
;; move all the items in one group to the other 
;; group
(defn union [state i j]
  (let [igroup (nth state i)
        jgroup (nth state j)] 
       (map #(if (= % jgroup) igroup %) state)))

;; first part of slide 4
(def newstate1 
  (-> no-connections
      (union 4 3)
      (union 3 8)
      (union 6 5)
      (union 9 4)
      (union 2 1)))

(connected? newstate1 0 7)
(connected? newstate1 8 9)

;; second part of slide 4
(def newstate2 
  (-> newstate1
      (union 5 0)
      (union 7 2)
      (union 6 1)
      (union 1 0)))

(connected? newstate2 0 7)
(connected? newstate2 8 9)