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to Poker in the Clojure Track

Published at Feb 04 2021 · 0 comments
Test suite

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

See wikipedia for an overview of poker hands.


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.


(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)

(def ranks ["2" "3" "4" "5" "6" "7" "8" "9" "10" "J" "Q" "K" "A"])
(def suits [\H \S \D \C])

(defn card [s]
  (let [rank (apply str (butlast s))
        suit (last s)
        weight (inc (.indexOf ranks rank))]
    {:rank rank
     :suit suit
     :weight weight
     :alt-weight (if (= rank "A")

(defn normalize-hand [h]
  (->> (clojure.string/split h #" ")
       (map card)))

(defn group-sizes [h attr]
  (->> h
       (group-by attr)
       (map #(count (second %)))))

(defn largest-group [h attr]
  (apply max (group-sizes h attr)))

(defn largest-weight-diff [h w]
  (->> h
     (sort-by w)
     (map w)
     (partition 2 1)
     (map (partial reduce -))
     (apply max)))

(defn flush? [h]
  (= 5 (largest-group h :suit)))

(defn straight? 
  ([h] (straight? h :weight))
  ([h w]
   (= 1 (largest-weight-diff h w))))

(defn straight-flush? 
  ([h] (straight-flush? h :weight))
  ([h w]
   (and (straight? h w)
        (flush? h))))

(defn four-of-a-kind? [h]
  (= 4 (largest-group h :rank)))

(defn full-house? [h]
  (= #{2 3} (set (group-sizes h :rank))))

(defn three-of-a-kind? [h]
  (= #{1 3} (set (group-sizes h :rank))))

(defn two-pair? [h]
  (= [1 2 2] (sort (group-sizes h :rank))))

(defn one-pair? [h]
  (= [1 1 1 2] (sort (group-sizes h :rank))))

(defn n-plet-weight 
  ([h n] (n-plet-weight h n :weight))
  ([h n w]
   (->> h
        (group-by w)
        (map #(vector (first %) (count (second %))))
        (filter #(= n (second %)))
        (map first)

(defn hand-score [h]
    (straight-flush? h) (concat [8] (n-plet-weight h 1))
    (straight-flush? h :alt-weight) (concat [8] (n-plet-weight h 1 :alt-weight))
    (four-of-a-kind? h) (concat [7] (n-plet-weight h 4) (n-plet-weight h 1))
    (full-house? h) (concat [6] (n-plet-weight h 3) (n-plet-weight h 2))
    (flush? h) (concat [5] (n-plet-weight h 1))
    (straight? h) (concat [4] (n-plet-weight h 1))
    (straight? h :alt-weight) (concat [4] (n-plet-weight h 1 :alt-weight))
    (three-of-a-kind? h) (concat [3] (n-plet-weight h 3) (n-plet-weight h 1))
    (two-pair? h) (concat [2] (n-plet-weight h 2) (n-plet-weight h 1))
    (one-pair? h) (concat [1] (n-plet-weight h 2) (n-plet-weight h 1))
    :else (concat [0] (n-plet-weight h 1))))

(defn compare-scores [s1 s2]
  (let [compare-len (min (count s1) (count s2))]
     (into [] (take compare-len s1))
     (into [] (take compare-len s2)))))

(defn make-hand [h]
  {:hand h
   :score (->> h

(defn best-hands [hands]
  (let [ordered-hands (->> hands
                   (map make-hand)
                   (sort-by :score compare-scores)
        top-hand-score (:score (first ordered-hands))]
    (->> ordered-hands
         (take-while #(= (:score %) top-hand-score))
         (map :hand))))

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