Implementation for 22a

challenge/day22/a.go

@@ -0,0 +1,98 @@
+package day22
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/nlowe/aoc2019/challenge"
+	"github.com/spf13/cobra"
+)
+
+var A = &cobra.Command{
+	Use:   "22a",
+	Short: "Day 22, Problem A",
+	Run: func(_ *cobra.Command, _ []string) {
+		fmt.Printf("Answer: %d\n", a(challenge.FromFile()))
+	},
+}
+
+const (
+	instrDealNewStack      = "deal into new stack"
+	instrCut               = "cut "
+	instrDealWithIncrement = "deal with increment "
+)
+
+var deckSize = 10007
+
+func a(challenge *challenge.Input) int {
+	deck := fancyShuffle(challenge)
+
+	for i, v := range deck {
+		if v == 2019 {
+			return i
+		}
+	}
+
+	panic("no solution")
+}
+
+func fancyShuffle(challenge *challenge.Input) []int {
+	deck := make([]int, deckSize)
+	for i := range deck {
+		deck[i] = i
+	}
+
+	for instruction := range challenge.Lines() {
+		if instruction == instrDealNewStack {
+			deck = dealIntoNewStack(deck)
+		} else if strings.HasPrefix(instruction, instrCut) {
+			n, err := strconv.Atoi(strings.TrimPrefix(instruction, instrCut))
+			if err != nil {
+				panic(err)
+			}
+
+			deck = cut(deck, n)
+		} else if strings.HasPrefix(instruction, instrDealWithIncrement) {
+			increment, err := strconv.Atoi(strings.TrimPrefix(instruction, instrDealWithIncrement))
+			if err != nil {
+				panic(err)
+			}
+
+			deck = dealWithIncrement(deck, increment)
+		}
+	}
+
+	return deck
+}
+
+func dealIntoNewStack(deck []int) []int {
+	newStack := make([]int, len(deck))
+	for i, v := range deck {
+		newStack[len(newStack)-i-1] = v
+	}
+
+	return newStack
+}
+
+func cut(deck []int, n int) []int {
+	newStack := make([]int, len(deck))
+	for i := range deck {
+		if n > 0 {
+			newStack[i] = deck[(n+i)%len(deck)]
+		} else {
+			newStack[i] = deck[(len(deck)+i+n)%len(deck)]
+		}
+	}
+
+	return newStack
+}
+
+func dealWithIncrement(deck []int, increment int) []int {
+	newStack := make([]int, len(deck))
+	for i := range deck {
+		newStack[(i*increment)%len(deck)] = deck[i]
+	}
+
+	return newStack
+}

challenge/day22/a_test.go

@@ -0,0 +1,44 @@
+package day22
+
+import (
+	"testing"
+
+	"github.com/nlowe/aoc2019/challenge"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFancyShuffle(t *testing.T) {
+	deckSize = 10
+	for _, tt := range []struct {
+		instructions string
+		expected     []int
+	}{
+		{instructions: "deal into new stack", expected: []int{9, 8, 7, 6, 5, 4, 3, 2, 1, 0}},
+		{instructions: "cut 3", expected: []int{3, 4, 5, 6, 7, 8, 9, 0, 1, 2}},
+		{instructions: "cut -4", expected: []int{6, 7, 8, 9, 0, 1, 2, 3, 4, 5}},
+		{instructions: "deal with increment 3", expected: []int{0, 7, 4, 1, 8, 5, 2, 9, 6, 3}},
+		{instructions: `deal with increment 7
+deal into new stack
+deal into new stack`, expected: []int{0, 3, 6, 9, 2, 5, 8, 1, 4, 7}},
+		{instructions: `cut 6
+deal with increment 7
+deal into new stack`, expected: []int{3, 0, 7, 4, 1, 8, 5, 2, 9, 6}},
+		{instructions: `deal with increment 7
+deal with increment 9
+cut -2`, expected: []int{6, 3, 0, 7, 4, 1, 8, 5, 2, 9}},
+		{instructions: `deal into new stack
+cut -2
+deal with increment 7
+cut 8
+cut -4
+deal with increment 7
+cut 3
+deal with increment 9
+deal with increment 3
+cut -1`, expected: []int{9, 2, 5, 8, 1, 4, 7, 0, 3, 6}},
+	} {
+		t.Run(tt.instructions, func(t *testing.T) {
+			require.Equal(t, tt.expected, fancyShuffle(challenge.FromLiteral(tt.instructions)))
+		})
+	}
+}

challenge/day22/input.txt

@@ -0,0 +1,100 @@
+deal with increment 16
+cut -7810
+deal with increment 70
+cut 8978
+deal into new stack
+deal with increment 14
+cut 9822
+deal with increment 31
+cut -3630
+deal with increment 37
+cut -929
+deal with increment 74
+cut -9268
+deal with increment 47
+cut -7540
+deal with increment 13
+cut -5066
+deal with increment 73
+cut 1605
+deal into new stack
+cut 1615
+deal with increment 72
+cut 1025
+deal with increment 28
+cut 6427
+deal with increment 10
+deal into new stack
+cut -8336
+deal with increment 33
+cut -9834
+deal with increment 64
+deal into new stack
+deal with increment 42
+cut 7013
+deal into new stack
+deal with increment 55
+deal into new stack
+cut 8349
+deal into new stack
+deal with increment 41
+cut -9073
+deal with increment 11
+deal into new stack
+deal with increment 46
+cut 613
+deal with increment 66
+cut 4794
+deal with increment 3
+cut -6200
+deal with increment 52
+deal into new stack
+cut 1328
+deal with increment 29
+cut -1670
+deal into new stack
+cut -706
+deal with increment 66
+cut -2827
+deal with increment 6
+cut 8493
+deal with increment 10
+deal into new stack
+deal with increment 75
+cut 3163
+deal with increment 14
+cut 4848
+deal with increment 66
+deal into new stack
+deal with increment 52
+deal into new stack
+deal with increment 71
+deal into new stack
+deal with increment 50
+cut -9466
+deal with increment 46
+cut -9621
+deal into new stack
+deal with increment 14
+deal into new stack
+cut 7236
+deal with increment 71
+cut -9836
+deal with increment 16
+deal into new stack
+cut -1519
+deal with increment 53
+cut -5190
+deal with increment 68
+cut 4313
+deal into new stack
+deal with increment 39
+deal into new stack
+deal with increment 5
+cut 3476
+deal with increment 61
+cut -2533
+deal with increment 10
+cut 4921
+deal with increment 67
+cut 3563

main.go

@@ -18,6 +18,7 @@ import (
 	"github.com/nlowe/aoc2019/challenge/day2"
 	"github.com/nlowe/aoc2019/challenge/day20"
 	"github.com/nlowe/aoc2019/challenge/day21"
+	"github.com/nlowe/aoc2019/challenge/day22"
 	"github.com/nlowe/aoc2019/challenge/day3"
 	"github.com/nlowe/aoc2019/challenge/day4"
 	"github.com/nlowe/aoc2019/challenge/day5"
@@ -83,6 +84,7 @@ func init() {
 		day19.A, day19.B,
 		day20.A, day20.B,
 		day21.A, day21.B,
+		day22.A,
 	)
 
 	flags := rootCmd.PersistentFlags()