same-game functional merge board-left

core.clj

(ns dummy.core
  :use [[clojure.contrib.seq-utils :only [indexed]]])

(defn find-all
  [coll x]
  (keep-indexed #(if (= x %2) %1) coll))

(defn merge-left-row [coll idx]
  (let [front (map second
                   (filter #(not (contains? idx (first %)))
                           (take (count coll) (indexed coll))))]
    (concat front (take (- (count coll) (count front))
                        (repeat nil)))))

(defn merge-left [coll]
  (let [idx (apply sorted-set (find-all (last coll) nil))]
    (map merge-left-row coll (repeat idx))))