Implement Poker Practice Exercise

config.json

@@ -1573,6 +1573,20 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "poker",
+        "name": "Poker",
+        "uuid": "56f78d43-4715-4e0b-80e9-b257b966db12",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4,
+        "topics": [
+          "arrays",
+          "conditionals",
+          "filtering",
+          "games"
+        ]
+      },
       {
         "slug": "yacht",
         "name": "Yacht",

exercises/practice/poker/.docs/instructions.md

@@ -0,0 +1,7 @@
+# Instructions
+
+Pick the best hand(s) from a list of poker hands.
+
+See [Wikipedia][poker-hands] for an overview of poker hands.
+
+[poker-hands]: https://en.wikipedia.org/wiki/List_of_poker_hands

exercises/practice/poker/.meta/config.json

@@ -0,0 +1,30 @@
+{
+  "authors": [
+    "thibault2705"
+  ],
+  "contributors": [
+    "SleeplessByte"
+  ],
+  "files": {
+    "solution": [
+      "poker.ts"
+    ],
+    "test": [
+      "poker.test.ts"
+    ],
+    "example": [
+      ".meta/proof.ci.ts"
+    ]
+  },
+  "blurb": "Pick the best hand(s) from a list of poker hands.",
+  "source": "Inspired by the training course from Udacity.",
+  "source_url": "https://www.udacity.com/course/design-of-computer-programs--cs212",
+  "custom": {
+    "version.tests.compatibility": "jest-29",
+    "flag.tests.task-per-describe": false,
+    "flag.tests.may-run-long": false,
+    "flag.tests.includes-optional": false,
+    "flag.tests.jest": true,
+    "flag.tests.tstyche": false
+  }
+}

exercises/practice/poker/.meta/proof.ci.ts

@@ -0,0 +1,234 @@
+export function bestHands(hands: string[]): string[] {
+  const parsed = hands.map((hand) => ({
+    original: hand,
+    score: evaluateHand(hand),
+  }))
+
+  let best = parsed[0]
+
+  for (const current of parsed.slice(1)) {
+    if (compareScores(current.score, best.score) > 0) {
+      best = current
+    }
+  }
+
+  return parsed
+    .filter((hand) => compareScores(hand.score, best.score) === 0)
+    .map((hand) => hand.original)
+}
+
+type Card = {
+  rank: number
+  suit: string
+}
+
+type HandScore = {
+  category: number
+  tiebreakers: number[]
+}
+
+function evaluateHand(hand: string): HandScore {
+  const cards = parseHand(hand)
+  const ranks = cards.map((c) => c.rank)
+  const sortedRanksDesc = [...ranks].sort((a, b) => b - a)
+
+  const flush = isFlush(cards)
+  const straightHigh = getStraightHigh(ranks)
+
+  const counts = getRankCounts(ranks)
+  const groups = Object.entries(counts)
+    .map(([rank, count]) => ({
+      rank: Number(rank),
+      count,
+    }))
+    .sort((a, b) => {
+      if (b.count !== a.count) return b.count - a.count
+      return b.rank - a.rank
+    })
+
+  // Straight flush
+  if (flush && straightHigh !== null) {
+    return {
+      category: 8,
+      tiebreakers: [straightHigh],
+    }
+  }
+
+  // Four of a kind
+  if (groups[0].count === 4) {
+    const quadRank = groups[0].rank
+    const kicker = groups[1].rank
+    return {
+      category: 7,
+      tiebreakers: [quadRank, kicker],
+    }
+  }
+
+  // Full house
+  if (groups[0].count === 3 && groups[1].count === 2) {
+    return {
+      category: 6,
+      tiebreakers: [groups[0].rank, groups[1].rank],
+    }
+  }
+
+  // Flush
+  if (flush) {
+    return {
+      category: 5,
+      tiebreakers: sortedRanksDesc,
+    }
+  }
+
+  // Straight
+  if (straightHigh !== null) {
+    return {
+      category: 4,
+      tiebreakers: [straightHigh],
+    }
+  }
+
+  // Three of a kind
+  if (groups[0].count === 3) {
+    const tripRank = groups[0].rank
+    const kickers = groups
+      .filter((g) => g.count === 1)
+      .map((g) => g.rank)
+      .sort((a, b) => b - a)
+
+    return {
+      category: 3,
+      tiebreakers: [tripRank, ...kickers],
+    }
+  }
+
+  // Two pair
+  if (groups[0].count === 2 && groups[1].count === 2) {
+    const pairRanks = groups
+      .filter((g) => g.count === 2)
+      .map((g) => g.rank)
+      .sort((a, b) => b - a)
+
+    const kicker = groups.find((g) => g.count === 1)!.rank
+
+    return {
+      category: 2,
+      tiebreakers: [...pairRanks, kicker],
+    }
+  }
+
+  // One pair
+  if (groups[0].count === 2) {
+    const pairRank = groups[0].rank
+    const kickers = groups
+      .filter((g) => g.count === 1)
+      .map((g) => g.rank)
+      .sort((a, b) => b - a)
+
+    return {
+      category: 1,
+      tiebreakers: [pairRank, ...kickers],
+    }
+  }
+
+  // High card
+  return {
+    category: 0,
+    tiebreakers: sortedRanksDesc,
+  }
+}
+
+function parseHand(hand: string): Card[] {
+  return hand.split(' ').map(parseCard)
+}
+
+function parseCard(card: string): Card {
+  const suit = card.slice(-1)
+  const rankText = card.slice(0, -1)
+
+  return {
+    rank: parseRank(rankText),
+    suit,
+  }
+}
+
+function parseRank(rank: string): number {
+  switch (rank) {
+    case 'J':
+      return 11
+    case 'Q':
+      return 12
+    case 'K':
+      return 13
+    case 'A':
+      return 14
+    default:
+      return Number(rank)
+  }
+}
+
+function isFlush(cards: Card[]): boolean {
+  return cards.every((card) => card.suit === cards[0].suit)
+}
+
+function getRankCounts(ranks: number[]): Record<number, number> {
+  const counts: Record<number, number> = {}
+
+  for (const rank of ranks) {
+    counts[rank] = (counts[rank] ?? 0) + 1
+  }
+
+  return counts
+}
+
+function getStraightHigh(ranks: number[]): number | null {
+  const unique = [...new Set(ranks)].sort((a, b) => a - b)
+
+  if (unique.length !== 5) {
+    return null
+  }
+
+  // Normal straight
+  let isSequential = true
+  for (let i = 1; i < unique.length; i++) {
+    if (unique[i] !== unique[i - 1] + 1) {
+      isSequential = false
+      break
+    }
+  }
+
+  if (isSequential) {
+    return unique[4]
+  }
+
+  // Ace-low straight: A,2,3,4,5
+  const aceLow = [2, 3, 4, 5, 14]
+  const isAceLow =
+    unique.length === aceLow.length &&
+    unique.every((value, index) => value === aceLow[index])
+
+  if (isAceLow) {
+    return 5
+  }
+
+  return null
+}
+
+function compareScores(a: HandScore, b: HandScore): number {
+  if (a.category !== b.category) {
+    return a.category - b.category
+  }
+
+  const maxLen = Math.max(a.tiebreakers.length, b.tiebreakers.length)
+
+  for (let i = 0; i < maxLen; i++) {
+    const av = a.tiebreakers[i] ?? 0
+    const bv = b.tiebreakers[i] ?? 0
+
+    if (av !== bv) {
+      return av - bv
+    }
+  }
+
+  return 0
+}