Hackerrank Luck Balance

Challenge

Prikshet’s solution

With feedback from noisesmith from the Clojurians Slack channel.

(defn luck-balance
  "Complexity: O(n), (= n (count contests))
  TOC: >2h"
  [k contests]
  (letfn [(sum-firsts [coll]
            (apply + (map first coll)))]
    (let [unimportant (filter (comp zero? second) contests)
          unimportant-sum (sum-firsts unimportant)
          sorted-important (->> contests
                              (filter #(= 1 (second %)))
                              (sort))
          k-sum (sum-firsts (take (- (count sorted-important) k) sorted-important))
          remaining-sum (sum-firsts (drop (- (count sorted-important) k) sorted-important))]
      (- (+ unimportant-sum
            remaining-sum)
         k-sum))))