Day 7 solutions ☀☀☀

day_7/compare.ts

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+export enum RANK {
+  FIVE_OF_A_KIND,
+  FOUR_OF_A_KIND,
+  FULL_HOUSE,
+  THREE_OF_A_KIND,
+  TWO_PAIR,
+  ONE_PAIR,
+  HIGH_CARD,
+}
+
+export const cmp_by_card = (
+  hand1: string,
+  hand2: string,
+  strength_order: Map<string, number>
+) => {
+  for (var i = 0; i < hand1.length; i++) {
+    const s1 = strength_order.get(hand1[i]);
+    const s2 = strength_order.get(hand2[i]);
+    if (undefined === s1 || undefined === s2) {
+      console.error("ERROR", i, hand1[i], hand2[i]);
+      return 0;
+    }
+    if (s1 > s2) return -1;
+    if (s1 < s2) return 1;
+  }
+  return 0;
+};

day_7/parser.ts

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+import * as fs from "fs";
+
+export interface HandBid {
+  hand: string;
+  bid: number;
+}
+
+export const read_file = (): HandBid[] =>
+  fs
+    .readFileSync("input", "ascii")
+    .split("\n")
+    .map((line) => {
+      const [hand, bid] = line.split(" ");
+      return { hand: hand, bid: Number.parseInt(bid) };
+    });

day_7/part_1.ts

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+import { RANK, cmp_by_card } from "./compare";
+import { HandBid, read_file } from "./parser";
+
+const rank_hand = (hand: string) => {
+  const cards = hand.split("");
+  const card_count = cards.reduce((count, char) => {
+    const c = count.get(char);
+    return c ? count.set(char, c + 1) : count.set(char, 1);
+  }, new Map<string, number>());
+
+  const unique_cards = Array.from(card_count.keys());
+
+  if (unique_cards.length === 1) return RANK.FIVE_OF_A_KIND;
+  if (unique_cards.length === 4) return RANK.ONE_PAIR;
+  if (unique_cards.length === 5) return RANK.HIGH_CARD;
+  if (
+    unique_cards.length === 2 &&
+    [1, 4].includes(card_count.get(unique_cards[0]) || 0)
+  )
+    return RANK.FOUR_OF_A_KIND;
+  if (
+    unique_cards.length === 2 &&
+    [2, 3].includes(card_count.get(unique_cards[0]) || 0)
+  )
+    return RANK.FULL_HOUSE;
+  if (
+    unique_cards.length === 3 &&
+    unique_cards.reduce((c, card) => card_count.get(card) === 3 || c, false)
+  )
+    return RANK.THREE_OF_A_KIND;
+
+  return RANK.TWO_PAIR;
+};
+
+const STRENGTH = new Map<string, number>(
+  Object.entries({
+    A: 0,
+    K: 1,
+    Q: 2,
+    J: 3,
+    T: 4,
+    "9": 5,
+    "8": 6,
+    "7": 7,
+    "6": 8,
+    "5": 9,
+    "4": 10,
+    "3": 11,
+    "2": 12,
+  })
+);
+
+const cmp_hand = (hand_bid1: HandBid, hand_bid2: HandBid) => {
+  if (rank_hand(hand_bid1.hand) > rank_hand(hand_bid2.hand)) return -1;
+  if (rank_hand(hand_bid1.hand) < rank_hand(hand_bid2.hand)) return 1;
+  return cmp_by_card(hand_bid1.hand, hand_bid2.hand, STRENGTH);
+};
+
+const hand_bids = read_file();
+
+console.log(
+  hand_bids
+    .sort(cmp_hand)
+    .reduce((sum, hand_bid, i) => sum + hand_bid.bid * (1 + i), 0)
+);

day_7/part_2.ts

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+import { RANK, cmp_by_card } from "./compare";
+import { HandBid, read_file } from "./parser";
+
+const rank_hand = (hand: string) => {
+  const cards = hand.split("");
+  const card_count = cards.reduce((count, char) => {
+    const c = count.get(char);
+    return c ? count.set(char, c + 1) : count.set(char, 1);
+  }, new Map<string, number>(Object.entries({ J: 0 })));
+
+  // It is always the most optimal choice to greedily substitute J for the card with the most occurrences.
+  var max_card = "?";
+  Array.from(card_count.keys()).forEach((card) => {
+    if (
+      card !== "J" &&
+      (card_count.get(card) || 0) > (card_count.get(max_card) || 0)
+    ) {
+      max_card = card;
+    }
+  });
+
+  card_count.set(
+    max_card,
+    (card_count.get(max_card) || 0) + (card_count.get("J") || 0)
+  );
+  card_count.delete("J");
+
+  const unique_cards = Array.from(card_count.keys()).filter(
+    (card) => card !== "J"
+  );
+
+  if (unique_cards.length === 1) return RANK.FIVE_OF_A_KIND;
+  if (unique_cards.length === 4) return RANK.ONE_PAIR;
+  if (unique_cards.length === 5) return RANK.HIGH_CARD;
+  if (
+    unique_cards.length === 2 &&
+    [1, 4].includes(card_count.get(unique_cards[0]) || 0)
+  )
+    return RANK.FOUR_OF_A_KIND;
+  if (
+    unique_cards.length === 2 &&
+    [2, 3].includes(card_count.get(unique_cards[0]) || 0)
+  )
+    return RANK.FULL_HOUSE;
+  if (
+    unique_cards.length === 3 &&
+    unique_cards.reduce((c, card) => card_count.get(card) === 3 || c, false)
+  )
+    return RANK.THREE_OF_A_KIND;
+
+  return RANK.TWO_PAIR;
+};
+
+const STRENGTH = new Map<string, number>(
+  Object.entries({
+    A: 0,
+    K: 1,
+    Q: 2,
+    T: 3,
+    "9": 4,
+    "8": 5,
+    "7": 6,
+    "6": 7,
+    "5": 8,
+    "4": 9,
+    "3": 10,
+    "2": 11,
+    J: 12,
+  })
+);
+
+const cmp_hand = (hand_bid1: HandBid, hand_bid2: HandBid) => {
+  if (rank_hand(hand_bid1.hand) > rank_hand(hand_bid2.hand)) return -1;
+  if (rank_hand(hand_bid1.hand) < rank_hand(hand_bid2.hand)) return 1;
+  return cmp_by_card(hand_bid1.hand, hand_bid2.hand, STRENGTH);
+};
+
+console.log(
+  read_file()
+    .sort(cmp_hand)
+    .reduce((sum, hand_bid, i) => sum + hand_bid.bid * (1 + i), 0)
+);