Discussion on: Daily Challenge #258 - Ranking Poker Hands

[Mike Talbot ⭐]

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 ⭐]

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

Mike Talbot ・ Jun 16 ・ 6 min read

#javascript