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## to Poker in the Clojure Track

Published at Jan 08 2020 · 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"

(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"

(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"])))

(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 :refer [join split]]))

(def rank-values {\J 11 \Q 12 \K 13 \A 14})

(defn rank [card]
(if-let [a-rank (re-find #"\d+" card)]
(Integer/parseInt a-rank)
(get rank-values (first card))))

(defn suit [card]
(str (last card)))

(defn- pattern [hand]
(->> (map rank hand)
(frequencies)
(vals)
(sort >)))

(defn pair? [hand]
(= 2 (apply max (pattern hand))))

(defn three-of-a-kind? [hand]
(= '(3 1 1) (pattern hand)))

(defn four-of-a-kind? [hand]
(= '(4 1) (pattern hand)))

(defn flush? [hand]
(->> (map suit hand)
(apply =)))

(defn full-house? [hand]
(= '(3 2) (pattern hand)))

(defn two-pairs? [hand]
(= '(2 2 1) (pattern hand)))

(defn straight-variants [hand]
(let [ranks         (map rank hand)
low-ace-ranks (replace {14 1} ranks)]
[(sort ranks) (sort low-ace-ranks)]))

(defn straight-numbers? [coll]
(= coll (range (apply min coll) (inc (apply max coll)))))

(defn straight? [hand]
(->> (straight-variants hand)
(some straight-numbers?)))

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

(defn high-card? [_] true)

;; index is rank
(defn hand-chekcers-by-rank []
[high-card?       pair?           two-pairs?
three-of-a-kind? straight?       flush?
full-house?      four-of-a-kind? straight-flush?])

(defn hand-rank [hand]
(->> (hand-chekcers-by-rank)
(map-indexed (fn [i f] (if (f hand) i 0)))
(apply max)))

(defn hand-value [hand]
(vec ;; vec is crucial type for comparator
(if (straight? hand)
(->> (straight-variants hand)
(filter straight-numbers?)
(first))
(->> (group-by rank hand)
(map #(vector (count (last %)) (first %)))
(sort #(compare %2 %1))))))

(defn keep-max
[val xs]
(reduce (fn [xs b]
(if-let [a (first xs)]
(case (compare (val a) (val b))
1  xs
0  (conj xs b)
-1 [b])
[b])) [] xs))

(defn best-hands [hands]
(->> (map #(split % #"\s") hands)
(keep-max hand-rank)
(keep-max hand-value)
(map #(join \space %))))``````