⭐ Created part two solution for day 15 puzzle

internal/day15/day15_test.go

@@ -9,6 +9,7 @@ import (
 	"testing"
 
 	"source.toby3d.me/toby3d/adventofcode/internal/day15/part1"
+	"source.toby3d.me/toby3d/adventofcode/internal/day15/part2"
 )
 
 var input []byte
@@ -26,3 +27,8 @@ func Example() {
 	fmt.Println(part1.ParseSequence(bytes.NewReader(input)).Sum())
 	// Output: 514639
 }
+
+func Example_PartTwo() {
+	fmt.Println(part2.ParseSequence(bytes.NewReader(input)).Sum())
+	// Output: 279470
+}

internal/day15/part2/day15part2.go

@@ -0,0 +1,118 @@
+package part2
+
+import (
+	"bufio"
+	"bytes"
+	"io"
+	"slices"
+)
+
+type (
+	Sequence []Step
+
+	Step []byte
+
+	Lens struct {
+		label  []byte
+		length int
+	}
+)
+
+func (s Step) Sum() uint {
+	var result uint
+
+	for i := range s.Hash() {
+		result += uint(s[i])
+		result *= 17
+		result = result % 256
+	}
+
+	return result
+}
+
+func (s Step) IsRemove() bool {
+	return bytes.IndexByte(s, '-') != -1
+}
+
+func (s Step) IsMove() bool {
+	return bytes.IndexByte(s, '=') != -1
+}
+
+func (s Step) Hash() []byte {
+	return s[:max(bytes.IndexByte(s, '-'), bytes.IndexByte(s, '='))]
+}
+
+func (s Step) Length() int {
+	index := max(bytes.IndexByte(s, '-'), bytes.IndexByte(s, '='))
+	if index == len(s)-1 {
+		return 0
+	}
+
+	return int(s[index+1] - '0')
+}
+
+func (s Sequence) Sum() uint64 {
+	var boxes [256][]Lens
+
+	for i := range s {
+		box := &boxes[int(s[i].Sum())]
+		index := slices.IndexFunc(*box, func(l Lens) bool {
+			return bytes.Equal(l.label, s[i].Hash())
+		})
+
+		switch {
+		default:
+			continue
+		case s[i].IsRemove() && index != -1:
+			*box = slices.Delete(*box, index, index+1)
+		case s[i].IsMove():
+			if index != -1 {
+				(*box)[index] = Lens{
+					label:  s[i].Hash(),
+					length: s[i].Length(),
+				}
+			} else {
+				*box = append(*box, Lens{
+					label:  s[i].Hash(),
+					length: s[i].Length(),
+				})
+			}
+		}
+	}
+
+	var result int
+	for i := range boxes {
+		for j := range boxes[i] {
+			result += (i + 1) * (j + 1) * boxes[i][j].length
+		}
+	}
+
+	return uint64(result)
+}
+
+func ParseSequence(r io.Reader) Sequence {
+	scanner := bufio.NewScanner(r)
+	scanner.Split(bufio.ScanBytes)
+
+	seq := make(Sequence, 0)
+	step := make(Step, 0)
+
+	for scanner.Scan() {
+		b := scanner.Bytes()[0]
+		switch b {
+		case ',', '\n':
+			seq = append(seq, step)
+			step = make(Step, 0)
+
+			continue
+		}
+
+		step = append(step, b)
+	}
+
+	return seq
+}
+
+func (s Step) GoString() string {
+	return string(s)
+}

internal/day15/part2/day15part2_test.go

@@ -0,0 +1,95 @@
+package part2_test
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	"source.toby3d.me/toby3d/adventofcode/internal/day15/part2"
+)
+
+func TestStep_Hash(t *testing.T) {
+	t.Parallel()
+
+	for name, tc := range map[string]struct {
+		expect string
+		input  part2.Step
+	}{
+		"rn=1": {input: part2.Step("rn=1"), expect: "rn"},
+		"cm-":  {input: part2.Step("cm-"), expect: "cm"},
+		"qp=3": {input: part2.Step("qp=3"), expect: "qp"},
+		"cm=2": {input: part2.Step("cm=2"), expect: "cm"},
+		"qp-":  {input: part2.Step("qp-"), expect: "qp"},
+		"pc=4": {input: part2.Step("pc=4"), expect: "pc"},
+		"ot=9": {input: part2.Step("ot=9"), expect: "ot"},
+		"ab=5": {input: part2.Step("ab=5"), expect: "ab"},
+		"pc-":  {input: part2.Step("pc-"), expect: "pc"},
+		"pc=6": {input: part2.Step("pc=6"), expect: "pc"},
+		"ot=7": {input: part2.Step("ot=7"), expect: "ot"},
+	} {
+		name, tc := name, tc
+
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			if actual := string(tc.input.Hash()); actual != tc.expect {
+				t.Errorf("want '%s', got '%s'", tc.expect, actual)
+			}
+		})
+	}
+}
+
+func TestStep_Length(t *testing.T) {
+	t.Parallel()
+
+	for name, tc := range map[string]struct {
+		input  part2.Step
+		expect int
+	}{
+		"rn=1": {input: part2.Step("rn=1"), expect: 1},
+		"cm-":  {input: part2.Step("cm-"), expect: 0},
+		"qp=3": {input: part2.Step("qp=3"), expect: 3},
+		"cm=2": {input: part2.Step("cm=2"), expect: 2},
+		"qp-":  {input: part2.Step("qp-"), expect: 0},
+		"pc=4": {input: part2.Step("pc=4"), expect: 4},
+		"ot=9": {input: part2.Step("ot=9"), expect: 9},
+		"ab=5": {input: part2.Step("ab=5"), expect: 5},
+		"pc-":  {input: part2.Step("pc-"), expect: 0},
+		"pc=6": {input: part2.Step("pc=6"), expect: 6},
+		"ot=7": {input: part2.Step("ot=7"), expect: 7},
+	} {
+		name, tc := name, tc
+
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			if actual := tc.input.Length(); actual != tc.expect {
+				t.Errorf("want %d, got %d", tc.expect, actual)
+			}
+		})
+	}
+}
+
+func TestStep_IsRemove(t *testing.T) {
+	t.Parallel()
+
+	if actual := part2.Step("qp-").IsRemove(); !actual {
+		t.Errorf("want %t, got %t", true, actual)
+	}
+}
+
+func TestStep_IsMove(t *testing.T) {
+	t.Parallel()
+
+	if actual := part2.Step("rn=1").IsMove(); !actual {
+		t.Errorf("want %t, got %t", true, actual)
+	}
+}
+
+func Example() {
+	input := "rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7\n"
+	seq := part2.ParseSequence(strings.NewReader(input))
+
+	fmt.Println(seq.Sum())
+	// Output: 145
+}