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Daily Challenge #258 - Ranking Poker Hands

dev.to staff on June 15, 2020

A famous casino is suddenly faced with a sharp decline of their revenues. They decide to offer Texas hold'em also online. Can you help them by writ...

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Sam Ferree • Jun 15 '20 • Edited

Sad this is a bit too difficult for me to do with Befunge, even Funge++, but I did think it could work quite well if done functionally.

This C# solution seems to work, have not tested beyond the initial to test cases

Edit: Did not add HighCard rules....

using System;
using System.Collections.Generic;
using System.Linq;
using HandRule = System.Func<string[], bool>;
namespace ConsoleSandbox
{
  public class PokerRanker
  {
    public static List<char> Ranks = new List<char> { '2', '3', '4', '5', '6', '7', '8',
      '9', 'T', 'J', 'Q', 'K', 'A' };
    public static List<char> Suits = new List<char> { 'S', 'H', 'D', 'C' };

    public List<HandRule> Rules = new List<HandRule>();

    public PokerRanker()
    {
      var ranksRanked = new List<char>(Ranks);
      ranksRanked.Reverse();

      char[] invalidStraightStarts = { 'J', 'Q', 'K', 'A' };

      Rules.AddRange(ranksRanked.Except(invalidStraightStarts).Select(rank =>
        StraightFlush(rank)));

      Rules.AddRange(ranksRanked.SelectMany(fourRank =>
        ranksRanked.Except(new[] {fourRank}).Select(highCard =>
          FourOfAKind(fourRank, highCard))));

      Rules.Add(Flush());

      Rules.AddRange(ranksRanked.Except(invalidStraightStarts).Select(rank =>
        Straight(rank)));

      Rules.AddRange(ranksRanked.SelectMany(threeRank =>
        ranksRanked.Except(new[] { threeRank }).Select(highCard =>
        ThreeOfAKind(threeRank, highCard))));

      Rules.AddRange(ranksRanked.SelectMany(pairRank =>
        ranksRanked.Except(new[] { pairRank }).Select(highCard =>
        Pair(pairRank, highCard))));

      Rules.AddRange(ranksRanked.Select(rank =>
        HighCard(rank)));
    }

    public string Rank(string[] myHand, string[] theirHand)
    {
      var mine = Rules.FindIndex(rule => rule(myHand));
      var theirs = Rules.FindIndex(rule => rule(theirHand));
      return mine < theirs
        ? "Win!"
        : theirs < mine
          ? "Lose!"
          : "Draw!";
    }

    public HandRule HighCard(char rank) => hand =>
      hand.Any(card => card[0] == rank);

    public HandRule Pair(char pairRank, char highCard) => hand =>
      hand.Count(card => card[0] == pairRank) == 2
      && HighCard(highCard)(hand);

    public HandRule ThreeOfAKind(char threeRank, char highCard) => hand =>
      hand.Count(card => card[0] == threeRank) == 3
      && HighCard(highCard)(hand);

    public HandRule Straight(char startingRank) => hand =>
    {
      var start = Ranks.IndexOf(startingRank);
      var ranks = Ranks.GetRange(start, 5);
      return ranks.All(rank => hand.Any(card => card[0] == rank));
    };

    public HandRule Flush() => hand =>
      hand.All(card => card[1] == hand[0][1]);

    public HandRule FullHouse(char threeRank, char pairRank) => hand =>
      ThreeOfAKind(threeRank, threeRank)(hand) &&
      Pair(pairRank, pairRank)(hand);

    public HandRule FourOfAKind(char fourRank, char highCard) => hand =>
      hand.Count(card => card[0] == fourRank) == 4
      && hand.Any(card => card[0] == highCard);

    public HandRule StraightFlush(char startingRank) => hand =>
      Straight(startingRank)(hand)
      && Flush()(hand);
  }
}

Sam Ferree • Jun 15 '20

I think I also missed flush with high card... hrmm

Matt Ellen • Jun 16 '20 • Edited

Created a python version

link to gist if embed isn't working

use it like:

python rank.py AS AC 2H 2C KD JC JD QH JH AS

Mike Talbot ⭐ • Jun 15 '20 • Edited


function PokerHand(hand) {
    this.hand = hand
}
PokerHand.prototype.compareWith = function(hand) {
    return compareHands(this.hand, hand.hand || hand)
}

const order = "23456789TJQKA"
function getHandDetails(hand) {
    const cards = hand.split(" ")
    const faces = cards.map(a => String.fromCharCode([77 - order.indexOf(a[0])])).sort()
    const suits = cards.map(a => a[1]).sort()
    const counts = faces.reduce(count, {})
    const duplicates = Object.values(counts).reduce(count, {})
    const flush = suits[0] === suits[4]
    const first = faces[0].charCodeAt(0)
    //Also handle low straight
    const lowStraight = faces.join("") === "AJKLM"
    const straight = lowStraight || faces.every((f, index) => f.charCodeAt(0) - first === index)
    let rank =
        (flush && straight && 1) ||
        (duplicates[4] && 2) ||
        (duplicates[3] && duplicates[2] && 3) ||
        (flush && 4) ||
        (straight && 5) ||
        (duplicates[3] && 6) ||
        (duplicates[2] > 1 && 7) ||
        (duplicates[2] && 8) ||
        9

    return { rank, value: faces.sort(byCountFirst).join("") }

    function byCountFirst(a, b) {
        //Counts are in reverse order - bigger is better
        const countDiff = counts[b] - counts[a]
        if (countDiff) return countDiff // If counts don't match return
        if (lowStraight) {
            a = a === "A" ? "N" : a
            b = b === "A" ? "N" : b
        }
        return b > a ? -1 : b === a ? 0 : 1
    }
    function count(c, a) {
        c[a] = (c[a] || 0) + 1
        return c
    }
}

function compareHands(h1, h2) {
    let d1 = getHandDetails(h1)
    let d2 = getHandDetails(h2)
    if (d1.rank === d2.rank) {
        if (d1.value < d2.value) {
            return "WIN"
        } else if (d1.value > d2.value) {
            return "LOSE"
        } else {
            return "DRAW"
        }
    }
    return d1.rank < d2.rank ? "WIN" : "LOSE"
}

Mike Talbot ⭐ • Jun 16 '20

Real world Javascript map/reduce, solving the Poker Hand problem

Mike Talbot ・ Jun 16 ・ 6 min read

#javascript

bravemaster619 • Jun 15 '20

I once implemented with Node.js. It was a little bit complicated as I remember. I think there is no quick and easy solution.