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Hindol's solution

to Poker in the Clojure Track

Published at Feb 08 2019 · 0 comments
Instructions
Test suite
Solution

Pick the best hand(s) from a list of poker hands.

See wikipedia for an overview of poker hands.

Source

Inspired by the training course from Udacity. https://www.udacity.com/course/viewer#!/c-cs212/

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

poker_test.clj

(ns poker-test
  (:require [clojure.test :refer [deftest is]]
            [poker :refer [best-hands]]))

(defn f [xs ys] (= (sort (best-hands xs)) (sort ys)))

(deftest single-hand-always-wins
  (is (f ["4S 5S 7H 8D JC"] ["4S 5S 7H 8D JC"])))

(deftest highest-card-out-of-all-hands-wins
  (is (f ["4D 5S 6S 8D 3C"
          "2S 4C 7S 9H 10H"
          "3S 4S 5D 6H JH"]
         ["3S 4S 5D 6H JH"])))

(deftest a-tie-has-multiple-winners
  (is (f ["4D 5S 6S 8D 3C"
          "2S 4C 7S 9H 10H"
          "3S 4S 5D 6H JH"
          "3H 4H 5C 6C JD"]
         ["3S 4S 5D 6H JH"
          "3H 4H 5C 6C JD"])))

(deftest multiple-hands-with-the-same-high-cards-tie-compares-next-highest-ranked-down-to-last-card
  (is (f ["3S 5H 6S 8D 7H"
          "2S 5D 6D 8C 7S"]
         ["3S 5H 6S 8D 7H"])))

(deftest one-pair-beats-high-card
  (is (f ["4S 5H 6C 8D KH"
          "2S 4H 6S 4D JH"]
         ["2S 4H 6S 4D JH"])))

(deftest highest-pair-wins
  (is (f ["4S 2H 6S 2D JH"
          "2S 4H 6C 4D JD"]
         ["2S 4H 6C 4D JD"])))

(deftest two-pairs-beats-one-pair
  (is (f ["2S 8H 6S 8D JH"
          "4S 5H 4C 8C 5C"]
         ["4S 5H 4C 8C 5C"])))

(deftest both-hands-have-two-pairs-highest-ranked-pair-wins
  (is (f ["2S 8H 2D 8D 3H"
          "4S 5H 4C 8S 5D"]
         ["2S 8H 2D 8D 3H"])))

(deftest both-hands-have-two-pairs-with-the-same-highest-ranked-pair-tie-goes-to-low-pair
  (is (f ["2S QS 2C QD JH"
          "JD QH JS 8D QC"]
         ["JD QH JS 8D QC"])))

(deftest both-hands-have-two-identically-ranked-pairs-tie-goes-to-remaining-card-kicker
  (is (f ["JD QH JS 8D QC"
          "JS QS JC 2D QD"]
         ["JD QH JS 8D QC"])))

(deftest three-of-a-kind-beats-two-pair
  (is (f ["2S 8H 2H 8D JH"
          "4S 5H 4C 8S 4H"]
         ["4S 5H 4C 8S 4H"])))

(deftest both-hands-have-three-of-a-kind-tie-goes-to-highest-ranked-triplet
  (is (f ["2S 2H 2C 8D JH"
          "4S AH AS 8C AD"]
         ["4S AH AS 8C AD"])))

(deftest with-multiple-decks-two-players-can-have-same-three-of-a-kind-ties-go-to-highest-remaining-cards
  (is (f ["4S AH AS 7C AD"
          "4S AH AS 8C AD"]
         ["4S AH AS 8C AD"])))

(deftest a-straight-beats-three-of-a-kind
  (is (f ["4S 5H 4C 8D 4H"
          "3S 4D 2S 6D 5C"]
         ["3S 4D 2S 6D 5C"])))

(deftest aces-can-end-a-straight-10-J-Q-K-A
  (is (f ["4S 5H 4C 8D 4H"
          "10D JH QS KD AC"]
         ["10D JH QS KD AC"])))

(deftest aces-can-start-a-straight-A-2-3-4-5
  (is (f ["4S 5H 4C 8D 4H"
          "4D AH 3S 2D 5C"]
         ["4D AH 3S 2D 5C"])))

(deftest both-hands-with-a-straight-tie-goes-to-highest-ranked-card
  (is (f ["4S 6C 7S 8D 5H"
          "5S 7H 8S 9D 6H"]
         ["5S 7H 8S 9D 6H"])))

(deftest even-though-an-ace-is-usually-high-a-5-high-straight-is-the-lowest-scoring-straight
  (is (f ["2H 3C 4D 5D 6H"
          "4S AH 3S 2D 5H"]
         ["2H 3C 4D 5D 6H"])))

(deftest flush-beats-a-straight
  (is (f ["4C 6H 7D 8D 5H"
          "2S 4S 5S 6S 7S"]
         ["2S 4S 5S 6S 7S"])))

(deftest both-hands-have-a-flush-tie-goes-to-high-card-down-to-the-last-one-if-necessary
  (is (f ["4H 7H 8H 9H 6H"
          "2S 4S 5S 6S 7S"]
         ["4H 7H 8H 9H 6H"])))

(deftest full-house-beats-a-flush
  (is (f ["3H 6H 7H 8H 5H"
          "4S 5H 4C 5D 4H"]
         ["4S 5H 4C 5D 4H"])))

(deftest both-hands-have-a-full-house-tie-goes-to-highest-ranked-triplet
  (is (f ["4H 4S 4D 9S 9D"
          "5H 5S 5D 8S 8D"]
         ["5H 5S 5D 8S 8D"])))

(deftest with-multiple-decks-both-hands-have-a-full-house-with-the-same-triplet-tie-goes-to-the-pair
  (is (f ["5H 5S 5D 9S 9D"
          "5H 5S 5D 8S 8D"]
         ["5H 5S 5D 9S 9D"])))

(deftest four-of-a-kind-beats-a-full-house
  (is (f ["4S 5H 4D 5D 4H"
          "3S 3H 2S 3D 3C"]
         ["3S 3H 2S 3D 3C"])))

(deftest both-hands-have-four-of-a-kind-tie-goes-to-high-quad
  (is (f ["2S 2H 2C 8D 2D"
          "4S 5H 5S 5D 5C"]
         ["4S 5H 5S 5D 5C"])))

(deftest with-multiple-decks-both-hands-with-identical-four-of-a-kind-tie-determined-by-kicker
  (is (f ["3S 3H 2S 3D 3C"
          "3S 3H 4S 3D 3C"]
         ["3S 3H 4S 3D 3C"])))

(deftest straight-flush-beats-four-of-a-kind
  (is (f ["4S 5H 5S 5D 5C"
          "7S 8S 9S 6S 10S"]
         ["7S 8S 9S 6S 10S"])))

(deftest both-hands-have-straight-flush-tie-goes-to-highest-ranked-card
  (is (f ["4H 6H 7H 8H 5H"
          "5S 7S 8S 9S 6S"]
         ["5S 7S 8S 9S 6S"])))
(ns poker
  (:require [clojure.string :as str]))

(defn- str->rank
  [s]
  (case s
    "J" 11
    "Q" 12
    "K" 13
    "A" 14                   ; ace is normally high
    (Integer/parseInt s)))

(defn- str->card
  [s]
  {:rank (-> s drop-last str/join str->rank)
   :suit (-> s last str)})

(defn- parse-hand
  [s]
  (->> s
       (#(str/split % #" "))
       (map str->card)
       (sort-by :rank >)))

(defn- straight?
  [hand &
   {:keys [ace-low?]
    :or {ace-low? false}}]
  (->> (:ranks hand)
       (partition 2 1)
       (map (partial apply -))
       (#(if ace-low?                   ; ace can be both high and low
           (= '(9 1 1 1) %)
           (every? #{1} %)))))

(defn- flush?
  [hand]
  (->> (:suits hand)
       (count)
       (= 1)))

(defn- straight-flush?
  [hand]
  (and (straight? hand) (flush? hand)))

(defn- sort-key
  [hand]
  (let [ranks (mapv :rank hand)
        suits (distinct (map :suit hand))
        grouped (->> ranks
                     (group-by identity)
                     (mapv second)
                     (sort-by count >)
                     (into []))
        distrib (mapv count grouped)
        decorated {:cards hand
                   :ranks ranks
                   :suits suits}]
    [(if (straight-flush? decorated) (first ranks) 0)
     (if (= [4 1] distrib) grouped [])     ; four of a kind
     (if (= [3 2] distrib) grouped [])     ; full house
     (if (flush? decorated) ranks [])
     (if (straight? decorated)          ; try ace high first
       (first ranks)
       (if (straight? decorated :ace-low? true) 5 0)) ; then try ace low
     (if (= [3 1 1] distrib) grouped [])   ; three of a kind
     (if (= [2 2 1] distrib) grouped [])   ; two pair
     (if (= [2 1 1 1] distrib) grouped []) ; pair
     ranks]))                              ; high card

(defn best-hands
  [hands]
  (->> hands
       (group-by (comp sort-key parse-hand))
       (sort)
       (last)
       (second)))

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