#### Problem

In the card game poker, a hand consists of five cards and are ranked, from lowest to highest, in the following way:

High Card: Highest value card.One Pair: Two cards of the same value.Two Pairs: Two different pairs.Three of a Kind: Three cards of the same value.Straight: All cards are consecutive values.Flush: All cards of the same suit.Full House: Three of a kind and a pair.Four of a Kind: Four cards of the same value.Straight Flush: All cards are consecutive values of same suit.Royal Flush: Ten, Jack, Queen, King, Ace, in same suit.

The cards are valued in the order:

2, 3, 4, 5, 6, 7, 8, 9, 10, Jack, Queen, King, Ace.

If two players have the same ranked hands then the rank made up of the highest value wins; for example, a pair of eights beats a pair of fives (see example 1 below). But if two ranks tie, for example, both players have a pair of queens, then highest cards in each hand are compared (see example 4 below); if the highest cards tie then the next highest cards are compared, and so on.

Consider the following five hands dealt to two players:

The file,poker.txt, contains one-thousand random hands dealt to two players. Each line of the file contains ten cards (separated by a single space): the first five are Player 1’s cards and the last five are Player 2’s cards. You can assume that all hands are valid (no invalid characters or repeated cards), each player’s hand is in no specific order, and in each hand there is a clear winner.

How many hands does Player 1 win?

#### Solution

open System.IO // define the suits type Suit = | Heart | Club | Spade | Diamond // define the card values type CardValue = | ValueCard of int | Jack | Queen | King | Ace // define the + unary operator on the CardValue type static member (~+) (value:CardValue) = match value with | ValueCard n -> if n < 10 then ValueCard (n+1) else Jack | Jack -> Queen | Queen -> King | King -> Ace | Ace -> ValueCard(2) // define the Card type type Card = { Value:CardValue; Suit:Suit } // define the ranks type Rank = | HighCard of CardValue | OnePair of CardValue | TwoPairs of CardValue * CardValue | Three of CardValue | Straight of CardValue // highest value card | Flush | FullHouse of CardValue * CardValue | Four of CardValue | StraightFlush of CardValue // highest value card & suit | RoyalFlush // define function to check if cards are the same suit let isSameSuit (cards:Card list) = cards |> List.forall (fun c -> c.Suit = cards.Head.Suit) // define function to get the highest card let getHighestCard(cards:Card list) = cards |> List.maxBy (fun card -> card.Value) // define function to check if cards are a straight set let isStraight (cards:Card list) = let flag = cards |> List.sort |> Seq.windowed 2 |> Seq.forall (fun [|card1; card2|] -> card2.Value = +card1.Value) (flag, getHighestCard cards) // define function to get the duplicated cards let getDupes (cards:Card list) = cards |> Seq.groupBy (fun card -> card.Value) |> Seq.map (fun (k, seq) -> (k, Seq.length seq)) |> Seq.filter (fun (k, len) -> len > 1) |> Seq.toList // evaluate the given hand of cards to return the rank let evaluateHand (cards:Card list) = let (isStraight, highCard) = isStraight cards let sameSuit = isSameSuit cards if sameSuit && isStraight && highCard.Value = Ace then RoyalFlush else if sameSuit && isStraight then StraightFlush(highCard.Value) else if sameSuit then Flush else if isStraight then Straight(highCard.Value) else let dupes = getDupes cards if dupes.Length = 0 then HighCard(highCard.Value) else if dupes.Length = 1 then match dupes.[0] with | (cardValue,2) -> OnePair(cardValue) | (cardValue,3) -> Three(cardValue) | (cardValue,4) -> Four(cardValue) else match dupes with | [(cardValue',2);(cardValue'',2)] -> TwoPairs(cardValue', cardValue'') | [(cardValue',3);(cardValue'',2)] -> FullHouse(cardValue', cardValue'') | [(cardValue',2);(cardValue'',3)] -> FullHouse(cardValue'', cardValue') // define function to check if player 1 wins let isP1Winner (p1:Card list) (p2:Card list) = let p1Rank, p2Rank = evaluateHand p1, evaluateHand p2 if p1Rank > p2Rank then true else if p1Rank = p2Rank then let rec compareHighCard (p1':Card list) (p2':Card list) = let p1'HighCard, p2'HighCard = getHighestCard p1', getHighestCard p2' if p1'HighCard.Value > p2'HighCard.Value then true else if p1'HighCard.Value = p2'HighCard.Value then let p1'' = p1' |> List.filter (fun c -> c.Value < p1'HighCard.Value) let p2'' = p2' |> List.filter (fun c -> c.Value < p2'HighCard.Value) compareHighCard p1'' p2'' else false compareHighCard p1 p2 else false // define function to parse, say, "3D" into a 3 of Diamond let parseCard [|(value:char);(suit:char)|] = let cardValue = match value with | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' -> ValueCard(int(value.ToString())) | 'T' -> ValueCard(10) | 'J' -> Jack | 'Q' -> Queen | 'K' -> King | 'A' -> Ace let suit = match suit with | 'S' -> Spade | 'H' -> Heart | 'D' -> Diamond | 'C' -> Club { Card.Value=cardValue; Suit=suit } // get the array of all the dealt hands from the poker text file let hands = File.ReadAllLines(@"C:\TEMP\poker.txt") |> Array.map (fun str -> str.Split(' ') |> Array.map (fun str -> parseCard (str.ToCharArray()))) // separate the hands into two different arrays, one for player 1 and the other player 2 let p1Hands = hands |> Array.map (fun cards -> cards |> Seq.take 5 |> Seq.toList) let p2Hands = hands |> Array.map (fun cards -> cards |> Seq.skip 5 |> Seq.toList) let answer = Array.map2 (fun p1 p2 -> isP1Winner p1 p2) p1Hands p2Hands |> Array.filter (fun b -> b) |> Array.length

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That is a very clean solution. I like the use of the Rank type, much better than my approach. I ended up returning a large number plus the value of the highest card for each ranking.

For example a straight flush would be 8000 + the value of the highest card.