sis-email-algo.clj

(def idx-a {:a [[:a 1] [:a 2]]
            :b [[:b 3]]
            :c [[:c 4]]
            :d [[:d 2]]})
(def idx-b {1 [[:a 1]]
            2 [[:a 2] [:d 2]]
            3 [[:b 3]]
            4 [[:c 4]]})

(defn process-group
  [idx-a idx-b starting-k]
  (loop [cur-idx    idx-a
         nxt-idx    idx-b
         lookup-fns (cycle [second first])
         k's        #{starting-k}
         group      #{}]
    (let [at-k      (apply concat (vals (select-keys cur-idx k's)))
          new-group (apply conj group at-k)]
      (println "cur idx:" cur-idx)
      (println "nxt idx:" nxt-idx)
      (println "k's:" k's)
      (println "at-k:" at-k)
      (println "group:" group)

      (cond
        ;; Base case: no values were found by looking up all keys in the current
        ;; index, meaning there are no more values to process
        (empty? at-k)
        new-group

        ;; Recursive case: add all found values from the current index to the
        ;; group, remove all used keys from the current index, swap the indices,
        ;; and repeat
        :else
        (recur nxt-idx
               (apply dissoc cur-idx k's)
               (rest lookup-fns)
               (into #{} (map (first lookup-fns) new-group))
               (apply conj new-group at-k))))))