2020-day22: 537/997 recursive "war" card game. hard instructions to get right on the first go

2020/day22/main.go

@@ -5,7 +5,7 @@ import (
 	"fmt"
 	"strings"
 
-	"github.com/alexchao26/advent-of-code-go/mathutil"
+	"github.com/alexchao26/advent-of-code-go/cast"
 	"github.com/alexchao26/advent-of-code-go/util"
 )
 
@@ -15,32 +15,100 @@ func main() {
 	flag.Parse()
 	fmt.Println("Running part", part)
 
+	var ans int
 	if part == 1 {
-		ans := part1(util.ReadFile("./input.txt"))
-		util.CopyToClipboard(fmt.Sprintf("%v", ans))
-		fmt.Println("Output:", ans)
+		ans = part1(util.ReadFile("./input.txt"))
 	} else {
-		ans := part2(util.ReadFile("./input.txt"))
-		util.CopyToClipboard(fmt.Sprintf("%v", ans))
-		fmt.Println("Output:", ans)
+		ans = part2(util.ReadFile("./input.txt"))
 	}
+	fmt.Println("Output:", ans)
 }
 
+// leaderboard: 537
 func part1(input string) int {
-	parsed := parseInput(input)
-	_ = parsed
+	deck1, deck2 := parseInput(input)
 
-	return 0
+	for !(len(deck1) == 0 || len(deck2) == 0) {
+		top1, top2 := deck1[0], deck2[0]
+		if top1 > top2 {
+			deck1 = append(deck1, top1, top2)
+		} else {
+			deck2 = append(deck2, top2, top1)
+		}
+		deck1 = deck1[1:]
+		deck2 = deck2[1:]
+	}
+
+	winningDeck := append(deck1, deck2...)
+	var sumOfProducts int
+	multiplier := 1
+	for i := len(winningDeck) - 1; i >= 0; i-- {
+		sumOfProducts += multiplier * winningDeck[i]
+		multiplier++
+	}
+
+	return sumOfProducts
 }
 
 func part2(input string) int {
-	return 0
+	deck1, deck2 := parseInput(input)
+	winningScore, _ := recursiveGame(deck1, deck2)
+	return winningScore
 }
 
-func parseInput(input string) (ans []int) {
-	lines := strings.Split(input, "\n")
-	for _, l := range lines {
-		ans = append(ans, mathutil.StrToInt(l))
+// leaderboard: 997
+func recursiveGame(deck1, deck2 []int) (finalScore int, player1Wins bool) {
+	previousHands1 := map[string]bool{}
+	previousHands2 := map[string]bool{}
+
+	for !(len(deck1) == 0 || len(deck2) == 0) {
+		top1, top2 := deck1[0], deck2[0]
+
+		if previousHands1[fmt.Sprintf("%v", deck1)] || previousHands2[fmt.Sprintf("%v", deck2)] {
+			player1Wins = true
+		} else {
+			previousHands1[fmt.Sprintf("%v", deck1)] = true
+			previousHands2[fmt.Sprintf("%v", deck2)] = true
+
+			// if not enough cards in either deck, just compare cards
+			if top1 > len(deck1)-1 || top2 > len(deck2)-1 {
+				player1Wins = top1 > top2
+			} else {
+				// otherwise recurse
+				_, player1Wins = recursiveGame(append([]int{}, deck1[1:top1+1]...), append([]int{}, deck2[1:top2+1]...))
+			}
+		}
+
+		if player1Wins {
+			deck1 = append(deck1, top1, top2)
+		} else {
+			deck2 = append(deck2, top2, top1)
+		}
+
+		deck1 = deck1[1:]
+		deck2 = deck2[1:]
 	}
-	return ans
+
+	winningDeck := append(deck1, deck2...)
+	var sumOfProducts int
+	multiplier := 1
+	for i := len(winningDeck) - 1; i >= 0; i-- {
+		sumOfProducts += multiplier * winningDeck[i]
+		multiplier++
+	}
+
+	// player1Wins boolean is equivalent to if their deck does not have zero cards
+	return sumOfProducts, len(deck1) != 0 // 997
+}
+
+func parseInput(input string) ([]int, []int) {
+	players := strings.Split(input, "\n\n")
+	var deck1, deck2 []int
+	for _, l := range strings.Split(players[0], "\n")[1:] {
+		deck1 = append(deck1, cast.ToInt(l))
+	}
+	for _, l := range strings.Split(players[1], "\n")[1:] {
+		deck2 = append(deck2, cast.ToInt(l))
+	}
+	return deck1, deck2
 }

2020/day22/main_test.go

@@ -2,15 +2,32 @@ package main
 
 import (
 	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
 )
 
+var example = `Player 1:
+9
+2
+6
+3
+1
+
+Player 2:
+5
+8
+4
+7
+10`
+
 func Test_part1(t *testing.T) {
 	tests := []struct {
 		name  string
 		input string
 		want  int
 	}{
-		// {"actual", util.ReadFile("input.txt"), ACTUAL_ANSWER},
+		{"example", example, 306},
+		{"actual", util.ReadFile("input.txt"), 33403},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -27,7 +44,8 @@ func Test_part2(t *testing.T) {
 		input string
 		want  int
 	}{
-		// {"actual", util.ReadFile("input.txt"), ACTUAL_ANSWER},
+		{"example", example, 291},
+		{"actual", util.ReadFile("input.txt"), 29177},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {