Day 22: Part 1

Signed-off-by: James Griffin <james@unsupervised.ca>

main.go

@@ -3,7 +3,7 @@ package main
 import (
 	"fmt"
 
-	"github.com/thatguygriff/aoc2020/twentyone"
+	"github.com/thatguygriff/aoc2020/twentytwo"
 )
 
 func main() {
@@ -88,6 +88,9 @@ func main() {
 	// fmt.Println(twenty.PartTwo())
 
 	// Day 21
-	fmt.Println(twentyone.PartOne())
+	// fmt.Println(twentyone.PartOne())
-	fmt.Println(twentyone.PartTwo())
+	// fmt.Println(twentyone.PartTwo())
+
+	// Day 22
+	fmt.Println(twentytwo.PartOne())
 }

twentytwo/day_twentytwo.go

@@ -0,0 +1,103 @@
+package twentytwo
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+)
+
+type player struct {
+	deck []int
+}
+
+func (p *player) score() int {
+	score := 0
+	for i := 0; i < len(p.deck); i++ {
+		score += p.deck[i] * (len(p.deck) - i)
+	}
+
+	return score
+}
+
+type combat struct {
+	one, two player
+}
+
+func (c *combat) load(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	one := false
+	two := false
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		if scanner.Text() == "Player 1:" {
+			one = true
+			continue
+		}
+
+		if scanner.Text() == "" {
+			one = false
+			two = false
+			continue
+		}
+
+		if scanner.Text() == "Player 2:" {
+			two = true
+			continue
+		}
+
+		card, err := strconv.Atoi(scanner.Text())
+		if err != nil {
+			return err
+		}
+
+		if one {
+			c.one.deck = append(c.one.deck, card)
+		} else if two {
+			c.two.deck = append(c.two.deck, card)
+		}
+	}
+
+	return nil
+}
+
+func (c *combat) play() (round int) {
+	for {
+		round++
+
+		// play cards
+		played := []int{c.one.deck[0], c.two.deck[0]}
+		c.one.deck = c.one.deck[1:]
+		c.two.deck = c.two.deck[1:]
+
+		if played[0] > played[1] {
+			c.one.deck = append(c.one.deck, played[0], played[1])
+		} else if played[0] < played[1] {
+			c.two.deck = append(c.two.deck, played[1], played[0])
+		} else {
+			panic("TIES ARE LIKELY IN PART 2")
+		}
+
+		if len(c.one.deck) == 0 || len(c.two.deck) == 0 {
+			break
+		}
+	}
+
+	return round
+}
+
+// PartOne What is the winning player's score
+func PartOne() string {
+	c := combat{}
+	if err := c.load("twentytwo/input.txt"); err != nil {
+		return err.Error()
+	}
+
+	rounds := c.play()
+	return fmt.Sprintf("The game lasted %d rounds with a score of %d - %d", rounds, c.one.score(), c.two.score())
+}

twentytwo/day_twentytwo_test.go

@@ -0,0 +1,30 @@
+package twentytwo
+
+import "testing"
+
+func Test_load_combat(t *testing.T) {
+	c := combat{}
+	if err := c.load("sample.txt"); err != nil {
+		t.Logf(err.Error())
+		t.FailNow()
+	}
+
+	if len(c.one.deck) != 5 || len(c.two.deck) != 5 {
+		t.Logf("Expected decks of 5 and 5, got %d and %d", len(c.one.deck), len(c.two.deck))
+	}
+}
+
+func Test_combat_play(t *testing.T) {
+	c := combat{}
+	if err := c.load("sample.txt"); err != nil {
+		t.Logf(err.Error())
+		t.FailNow()
+	}
+
+	c.play()
+
+	if c.one.score() != 0 || c.two.score() != 306 {
+		t.Logf("Expected score of 0-306, got %d-%d", c.one.score(), c.two.score())
+		t.Fail()
+	}
+}

twentytwo/input.txt

@@ -0,0 +1,53 @@
+Player 1:
+19
+22
+43
+38
+23
+21
+2
+40
+31
+17
+27
+28
+35
+44
+41
+47
+50
+7
+39
+5
+42
+25
+33
+3
+48
+
+Player 2:
+16
+24
+36
+6
+34
+11
+8
+30
+26
+15
+9
+10
+14
+1
+12
+4
+32
+13
+18
+46
+37
+29
+20
+45
+49

twentytwo/sample.txt

@@ -0,0 +1,13 @@
+Player 1:
+9
+2
+6
+3
+1
+
+Player 2:
+5
+8
+4
+7
+10