finish day 15

README.md

@@ -1,7 +1,7 @@
 # Advent of Code 2023
 
 [![Tests](https://github.com/devries/advent_of_code_2023/actions/workflows/main.yml/badge.svg)](https://github.com/devries/advent_of_code_2023/actions/workflows/main.yml)
-[![Stars: 28](https://img.shields.io/badge/⭐_Stars-28-yellow)](https://adventofcode.com/2023)
+[![Stars: 30](https://img.shields.io/badge/⭐_Stars-30-yellow)](https://adventofcode.com/2023)
 
 ## Plan for This Year
 
@@ -243,3 +243,11 @@ the third run of my solution after compilation on my Raspberry Pi.
 
   While programming it seems like I don't really want to shift gears to ask AI
   for help.
+
+- [Day 15: Lens Library](https://adventofcode.com/2023/day/15) - [⭐ part 1](day15p1/solution.go), [⭐ part 2](day15p2/solution.go)
+
+  This was also a very straightforward problem, although I did have to fix a
+  number of bugs I introduced. This problem illustrates how a hash map works
+  and then requires operations on the hashmapped values. I created a Lens object
+  which I passed around by value, and forgot when I changed an attribute in that
+  object, I need to reassign it to the lens in the box array.

day15p1/solution.go

@@ -0,0 +1,31 @@
+package day15p1
+
+import (
+	"io"
+	"strings"
+
+	"aoc/utils"
+)
+
+func Solve(r io.Reader) any {
+	lines := utils.ReadLines(r)
+
+	steps := strings.Split(lines[0], ",")
+
+	var sum uint64
+	for _, s := range steps {
+		sum += uint64(elfHash(s))
+	}
+	return sum
+}
+
+func elfHash(s string) byte {
+	var res byte
+
+	for _, r := range s {
+		res += byte(r)
+		res *= 17
+	}
+
+	return res
+}

day15p1/solution_test.go

@@ -0,0 +1,54 @@
+package day15p1
+
+import (
+	"strings"
+	"testing"
+
+	"aoc/utils"
+)
+
+var testInput = `rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7`
+
+func TestSolve(t *testing.T) {
+	tests := []struct {
+		input  string
+		answer uint64
+	}{
+		{testInput, 1320},
+	}
+
+	if testing.Verbose() {
+		utils.Verbose = true
+	}
+
+	for _, test := range tests {
+		r := strings.NewReader(test.input)
+
+		result := Solve(r).(uint64)
+
+		if result != test.answer {
+			t.Errorf("Expected %d, got %d", test.answer, result)
+		}
+	}
+}
+
+func TestHash(t *testing.T) {
+	tests := []struct {
+		input  string
+		answer byte
+	}{
+		{"HASH", 52},
+	}
+
+	if testing.Verbose() {
+		utils.Verbose = true
+	}
+
+	for _, test := range tests {
+		result := elfHash(test.input)
+
+		if result != test.answer {
+			t.Errorf("Expected %d, got %d", test.answer, result)
+		}
+	}
+}

day15p2/solution.go

@@ -0,0 +1,89 @@
+package day15p2
+
+import (
+	"io"
+	"strconv"
+	"strings"
+
+	"aoc/utils"
+)
+
+func Solve(r io.Reader) any {
+	lines := utils.ReadLines(r)
+
+	steps := strings.Split(lines[0], ",")
+
+	boxes := make(map[byte][]Lens)
+	for _, s := range steps {
+		if strings.Contains(s, "=") {
+			parts := strings.Split(s, "=")
+			fl, err := strconv.Atoi(parts[1])
+			utils.Check(err, "unable to convert %s to integer", parts[1])
+
+			h := elfHash(parts[0])
+
+			lenses := boxes[h]
+			found := false
+			for i, l := range lenses {
+				if l.Label == parts[0] {
+					found = true
+					l.FocalLength = fl
+					lenses[i] = l
+					break
+				}
+			}
+
+			if !found {
+				newlenses := make([]Lens, len(lenses)+1)
+				copy(newlenses, lenses)
+				newlenses[len(lenses)] = Lens{parts[0], fl}
+				boxes[h] = newlenses
+			}
+		} else {
+			label, _ := strings.CutSuffix(s, "-")
+
+			h := elfHash(label)
+
+			lenses := boxes[h]
+
+			newlenses := make([]Lens, 0, len(lenses))
+			for _, l := range lenses {
+				if l.Label != label {
+					newlenses = append(newlenses, l)
+				}
+			}
+
+			boxes[h] = newlenses
+		}
+	}
+
+	// Find focusing power
+	var sum uint64
+
+	for i := 0; i < 256; i++ {
+		lenses := boxes[byte(i)]
+		if len(lenses) != 0 {
+			for j, l := range lenses {
+				boxpower := (uint64(i) + 1) * uint64((j+1)*l.FocalLength)
+				sum += boxpower
+			}
+		}
+	}
+	return sum
+}
+
+func elfHash(s string) byte {
+	var res byte
+
+	for _, r := range s {
+		res += byte(r)
+		res *= 17
+	}
+
+	return res
+}
+
+type Lens struct {
+	Label       string
+	FocalLength int
+}

day15p2/solution_test.go

@@ -0,0 +1,54 @@
+package day15p2
+
+import (
+	"strings"
+	"testing"
+
+	"aoc/utils"
+)
+
+var testInput = `rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7`
+
+func TestSolve(t *testing.T) {
+	tests := []struct {
+		input  string
+		answer uint64
+	}{
+		{testInput, 145},
+	}
+
+	if testing.Verbose() {
+		utils.Verbose = true
+	}
+
+	for _, test := range tests {
+		r := strings.NewReader(test.input)
+
+		result := Solve(r).(uint64)
+
+		if result != test.answer {
+			t.Errorf("Expected %d, got %d", test.answer, result)
+		}
+	}
+}
+
+func TestHash(t *testing.T) {
+	tests := []struct {
+		input  string
+		answer byte
+	}{
+		{"HASH", 52},
+	}
+
+	if testing.Verbose() {
+		utils.Verbose = true
+	}
+
+	for _, test := range tests {
+		result := elfHash(test.input)
+
+		if result != test.answer {
+			t.Errorf("Expected %d, got %d", test.answer, result)
+		}
+	}
+}