From 44fb58ff14ec3801372cf0b7a8aa7e43ca683e1d Mon Sep 17 00:00:00 2001
From: David Ashby <delta.mu.alpha@gmail.com>
Date: Tue, 22 Dec 2020 16:58:21 -0500
Subject: [PATCH] 22 done

---
 22/main.go | 155 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 155 insertions(+)
 create mode 100644 22/main.go

diff --git a/22/main.go b/22/main.go
new file mode 100644
index 0000000..e57cc0b
--- /dev/null
+++ b/22/main.go
@@ -0,0 +1,155 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"time"
+)
+
+func main() {
+	start := time.Now()
+	partOne()
+	duration := time.Since(start)
+	partTwo()
+	duration2 := time.Since(start)
+	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
+}
+
+type deck struct {
+	cards []int
+}
+
+type cacheKey struct {
+	one int
+	two int
+}
+
+func countWinningDeck(deck []int) int {
+	sum := 0
+	for i := range deck {
+		sum = sum + ((len(deck) - i) * deck[i])
+	}
+	return sum
+}
+
+// return values is who won/their score: true for player one, false for player two
+func playCombat(one, two []int) (bool, int) {
+	round := 0
+	for len(one) > 0 && len(two) > 0 {
+		round = round + 1
+		if one[0] > two[0] {
+			one = append(one[1:], one[0], two[0])
+			two = two[1:]
+		} else if one[0] < two[0] {
+			two = append(two[1:], two[0], one[0])
+			one = one[1:]
+		}
+	}
+	if len(one) == 0 {
+		return false, countWinningDeck(two)
+	}
+	return true, countWinningDeck(one)
+}
+
+func playRecursiveCombat(one, two []int) (bool, int) {
+	loopCache := make(map[cacheKey]bool, 0)
+	round := 0
+	for len(one) > 0 && len(two) > 0 {
+		// check for loops
+		if loopCache[cacheKey{one: countWinningDeck(one), two: countWinningDeck(two)}] {
+			return true, countWinningDeck(one)
+		}
+		loopCache[cacheKey{one: countWinningDeck(one), two: countWinningDeck(two)}] = true
+
+		// otherwise, play a round
+		round = round + 1
+		if len(one[1:]) >= one[0] && len(two[1:]) >= two[0] {
+			// fuckin' go slice internals
+			subDeckOne := make([]int, len(one))
+			subDeckTwo := make([]int, len(two))
+			copy(subDeckOne, one)
+			copy(subDeckTwo, two)
+			winner, _ := playRecursiveCombat(subDeckOne[1:one[0]+1], subDeckTwo[1:two[0]+1])
+			if winner { // p1 wins
+				one = append(one[1:], one[0], two[0])
+				two = two[1:]
+			} else { // p2 wins
+				two = append(two[1:], two[0], one[0])
+				one = one[1:]
+			}
+		} else if one[0] > two[0] {
+			one = append(one[1:], one[0], two[0])
+			two = two[1:]
+		} else if one[0] < two[0] {
+			two = append(two[1:], two[0], one[0])
+			one = one[1:]
+		}
+	}
+	if len(one) == 0 {
+		return false, countWinningDeck(two)
+	}
+	return true, countWinningDeck(one)
+}
+
+func partOne() {
+	f, _ := os.Open("input")
+	reader := bufio.NewReader(f)
+	scanner := bufio.NewScanner(reader)
+
+	// deal the decks
+	playerone := deck{}
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "" {
+			break
+		}
+		i, err := strconv.Atoi(line)
+		if err == nil {
+			playerone.cards = append(playerone.cards, i)
+		}
+	}
+	playertwo := deck{}
+	for scanner.Scan() {
+		line := scanner.Text()
+		i, err := strconv.Atoi(line)
+		if err == nil {
+			playertwo.cards = append(playertwo.cards, i)
+		}
+	}
+
+	// play a game and determine a winner
+	_, score := playCombat(playerone.cards, playertwo.cards)
+	fmt.Println(score)
+}
+
+func partTwo() {
+	f, _ := os.Open("testinput")
+	reader := bufio.NewReader(f)
+	scanner := bufio.NewScanner(reader)
+
+	// deal the decks
+	playerone := deck{}
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "" {
+			break
+		}
+		i, err := strconv.Atoi(line)
+		if err == nil {
+			playerone.cards = append(playerone.cards, i)
+		}
+	}
+	playertwo := deck{}
+	for scanner.Scan() {
+		line := scanner.Text()
+		i, err := strconv.Atoi(line)
+		if err == nil {
+			playertwo.cards = append(playertwo.cards, i)
+		}
+	}
+
+	_, score := playRecursiveCombat(playerone.cards, playertwo.cards)
+	fmt.Println(score)
+}