days 22, 23, and 24

Author: alokmenghrajani

day22/day22.go

@@ -0,0 +1,137 @@
+package day22
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/alokmenghrajani/adventofcode2020/utils"
+)
+
+func Part1(input string) int {
+	var player1 []int
+	var player2 []int
+
+	cards := strings.Split(input, "\n\n")
+	for _, line := range strings.Split(cards[0], "\n")[1:] {
+		player1 = append(player1, utils.MustAtoi(line))
+	}
+	for _, line := range strings.Split(cards[1], "\n")[1:] {
+		player2 = append(player2, utils.MustAtoi(line))
+	}
+
+	winner := combatPart1(player1, player2)
+
+	r := 0
+	f := 1
+	for i := len(winner) - 1; i >= 0; i-- {
+		r = r + winner[i]*f
+		f++
+	}
+	return r
+}
+
+func combatPart1(player1, player2 []int) []int {
+	for len(player1) > 0 && len(player2) > 0 {
+		top1 := player1[0]
+		player1 = player1[1:]
+
+		top2 := player2[0]
+		player2 = player2[1:]
+
+		if top1 > top2 {
+			player1 = append(player1, top1)
+			player1 = append(player1, top2)
+		} else {
+			player2 = append(player2, top2)
+			player2 = append(player2, top1)
+		}
+	}
+	if len(player1) > 0 {
+		return player1
+	}
+	if len(player2) > 0 {
+		return player2
+	}
+	panic("invalid state")
+}
+
+func Part2(input string) int {
+	var player1 []int
+	var player2 []int
+
+	cards := strings.Split(input, "\n\n")
+	for _, line := range strings.Split(cards[0], "\n")[1:] {
+		player1 = append(player1, utils.MustAtoi(line))
+	}
+	for _, line := range strings.Split(cards[1], "\n")[1:] {
+		player2 = append(player2, utils.MustAtoi(line))
+	}
+
+	_, winner := combatPart2(player1, player2)
+
+	r := 0
+	f := 1
+	for i := len(winner) - 1; i >= 0; i-- {
+		r = r + winner[i]*f
+		f++
+	}
+	return r
+}
+
+func intsToStrings(a []int) []string {
+	var r []string
+	for _, n := range a {
+		r = append(r, fmt.Sprintf("%d", n))
+	}
+	return r
+}
+
+func combatPart2(player1, player2 []int) (bool, []int) {
+	memoize := map[string]bool{}
+	for len(player1) > 0 && len(player2) > 0 {
+		t := strings.Join(intsToStrings(player1), ",")
+		if memoize[t] {
+			return true, player1
+		}
+		memoize[t] = true
+
+		t = strings.Join(intsToStrings(player2), ",")
+		if memoize[t] {
+			return true, player1
+		}
+		memoize[t] = true
+
+		top1 := player1[0]
+		player1 = player1[1:]
+
+		top2 := player2[0]
+		player2 = player2[1:]
+
+		var r bool
+		if len(player1) >= top1 && len(player2) >= top2 {
+			copyPlayer1 := make([]int, top1)
+			copy(copyPlayer1, player1)
+
+			copyPlayer2 := make([]int, top2)
+			copy(copyPlayer2, player2)
+
+			r, _ = combatPart2(copyPlayer1, copyPlayer2)
+		} else {
+			r = top1 > top2
+		}
+		if r {
+			player1 = append(player1, top1)
+			player1 = append(player1, top2)
+		} else {
+			player2 = append(player2, top2)
+			player2 = append(player2, top1)
+		}
+	}
+	if len(player1) > 0 {
+		return true, player1
+	}
+	if len(player2) > 0 {
+		return false, player2
+	}
+	panic("invalid state")
+}

day22/day22_test.go

@@ -0,0 +1,41 @@
+package day22
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestPart1(t *testing.T) {
+	r := Part1(`Player 1:
+9
+2
+6
+3
+1
+
+Player 2:
+5
+8
+4
+7
+10`)
+	require.Equal(t, 306, r)
+}
+
+func TestPart2(t *testing.T) {
+	r := Part2(`Player 1:
+9
+2
+6
+3
+1
+
+Player 2:
+5
+8
+4
+7
+10`)
+	require.Equal(t, 291, r)
+}

day22/input.txt

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

day23/day23.go

@@ -0,0 +1,124 @@
+package day23
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/alokmenghrajani/adventofcode2020/utils"
+)
+
+type cup struct {
+	id   int
+	next *cup
+}
+
+func Part1(input string) string {
+	var first *cup
+	var prev *cup
+	cups := map[int]*cup{}
+	max := 0
+	for _, n := range strings.Split(input, "") {
+		curr := &cup{
+			id: utils.MustAtoi(n),
+		}
+		max = utils.IntMax(max, curr.id)
+		cups[curr.id] = curr
+		if first == nil {
+			first = curr
+		} else {
+			prev.next = curr
+		}
+		prev = curr
+	}
+	prev.next = first
+
+	curr := first
+	for t := 0; t < 100; t++ {
+		// remove 3 cups
+		cup1 := curr.next
+		cup2 := cup1.next
+		cup3 := cup2.next
+		curr.next = cup3.next
+
+		n := curr.id
+		for {
+			n--
+			if n == 0 {
+				n = max
+			}
+			if n != cup1.id && n != cup2.id && n != cup3.id {
+				break
+			}
+		}
+
+		dest := cups[n]
+		cup3.next = dest.next
+		dest.next = cup1
+		curr = curr.next
+	}
+
+	r := ""
+	curr = cups[1].next
+	for curr != cups[1] {
+		r = fmt.Sprintf("%s%d", r, curr.id)
+		curr = curr.next
+	}
+
+	return r
+}
+
+func Part2(input string) int {
+	var first *cup
+	var prev *cup
+	cups := map[int]*cup{}
+	max := 0
+	for _, n := range strings.Split(input, "") {
+		curr := &cup{
+			id: utils.MustAtoi(n),
+		}
+		max = utils.IntMax(max, curr.id)
+		cups[curr.id] = curr
+		if first == nil {
+			first = curr
+		} else {
+			prev.next = curr
+		}
+		prev = curr
+	}
+	for len(cups) < 1_000_000 {
+		curr := &cup{
+			id: max + 1,
+		}
+		max = utils.IntMax(max, curr.id)
+		cups[curr.id] = curr
+		prev.next = curr
+		prev = curr
+	}
+	prev.next = first
+
+	curr := first
+	for t := 0; t < 10_000_000; t++ {
+		// remove 3 cups
+		cup1 := curr.next
+		cup2 := cup1.next
+		cup3 := cup2.next
+		curr.next = cup3.next
+
+		n := curr.id
+		for {
+			n--
+			if n == 0 {
+				n = max
+			}
+			if n != cup1.id && n != cup2.id && n != cup3.id {
+				break
+			}
+		}
+
+		dest := cups[n]
+		cup3.next = dest.next
+		dest.next = cup1
+		curr = curr.next
+	}
+	return cups[1].next.id * cups[1].next.next.id
+}

day23/day23_test.go

@@ -0,0 +1,17 @@
+package day23
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestPart1(t *testing.T) {
+	r := Part1(`389125467`)
+	require.Equal(t, "67384529", r)
+}
+
+func TestPart2(t *testing.T) {
+	r := Part2(`389125467`)
+	require.Equal(t, 149245887792, r)
+}

day23/input.txt

@@ -0,0 +1 @@
+583976241