Initial commit

.gitignore

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+# Created by https://www.toptal.com/developers/gitignore/api/go,macos
+# Edit at https://www.toptal.com/developers/gitignore?templates=go,macos
+
+### Go ###
+# If you prefer the allow list template instead of the deny list, see community template:
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+# Binaries for programs and plugins
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, built with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+
+# Dependency directories (remove the comment below to include it)
+# vendor/
+
+# Go workspace file
+go.work
+
+### macOS ###
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+.DS_Store
+.AppleDouble
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+
+# Icon must end with two \r
+Icon
+
+
+# Thumbnails
+._*
+
+# Files that might appear in the root of a volume
+.DocumentRevisions-V100
+.fseventsd
+.Spotlight-V100
+.TemporaryItems
+.Trashes
+.VolumeIcon.icns
+.com.apple.timemachine.donotpresent
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+# Directories potentially created on remote AFP share
+.AppleDB
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+Network Trash Folder
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+
+### macOS Patch ###
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+
+# End of https://www.toptal.com/developers/gitignore/api/go,macos

README.org

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+#+title: Readme
+

days/day1/README.org

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+#+title: December First challenge - Historian Hysteria
+
+* Blurb
+The *Chief Historian* is always present for the big Christmas sleigh launch, but
+nobody has seen him in months! Last anyone heard, he was visiting locations that
+are historically significant to the North Pole; a group of Senior Historians has
+asked you to accompany them as they check the places they think he was most
+likely to visit.
+
+As each location is checked, they will mark it on their list with a *star*. They
+figure the Chief Historian must be in one of the first fifty places they'll
+look, so in order to save Christmas, you need to help them get fifty stars on
+their list before Santa takes off on December 25th.
+
+Collect stars by solving puzzles. Two puzzles will be made available on each day
+in the Advent calendar; the second puzzle is unlocked when you complete the
+first. Each puzzle grants one star. Good luck!
+
+You haven't even left yet and the group of Elvish Senior Historians has already
+hit a problem: their list of locations to check is currently empty. Eventually,
+someone decides that the best place to check first would be the Chief
+Historian's office.
+
+Upon pouring into the office, everyone confirms that the Chief Historian is
+indeed nowhere to be found. Instead, the Elves discover an assortment of notes
+and lists of historically significant locations! This seems to be the planning
+the Chief Historian was doing before he left. Perhaps these notes can be used to
+determine which locations to search?
+
+Throughout the Chief's office, the historically significant locations are listed
+not by name but by a unique number called the location ID. To make sure they
+don't miss anything, The Historians split into two groups, each searching the
+office and trying to create their own complete list of location IDs.
+
+There's just one problem: by holding the two lists up side by side (your puzzle
+input), it quickly becomes clear that the lists aren't very similar. Maybe you
+can help The Historians reconcile their lists?
+
+* Example
+
+#+begin_example
+3   4
+4   3
+2   5
+1   3
+3   9
+3   3
+#+end_example
+
+Maybe the lists are only off by a small amount! To find out, pair up the numbers
+and measure how far apart they are. Pair up the *smallest number in the left list*
+with *the smallest number in the right list*, then the *second-smallest left number*
+with the *second-smallest right number*, and so on.
+
+Within each pair, figure out *how far apart* the two numbers are; you'll need to
+*add up all of those distances*. For example, if you pair up a =3= from the left
+list with a =7= from the right list, the distance apart is =4=; if you pair up a =9=
+with a =3=, the distance apart is =6=.
+
+In the example list above, the pairs and distances would be as follows:
+
++ The smallest number in the left list is 1, and the smallest number in the right list is 3. The distance between them is 2.
++ The second-smallest number in the left list is 2, and the second-smallest number in the right list is another 3. The distance between them is 1.
++ The third-smallest number in both lists is 3, so the distance between them is 0.
++ The next numbers to pair up are 3 and 4, a distance of 1.
++ The fifth-smallest numbers in each list are 3 and 5, a distance of 2.
++ Finally, the largest number in the left list is 4, while the largest number in the right list is 9; these are a distance 5 apart.
++ To find the total distance between the left list and the right list, add up
+  the distances between all of the pairs you found. In the example above, this
+  is 2 + 1 + 0 + 1 + 2 + 5, a total distance of 11!
+
+Your actual left and right lists contain many location IDs. What is the total distance between your lists?
+
+
+* Part 2
+
+Your analysis only confirmed what everyone feared: the two lists of location IDs are indeed very different.
+
+Or are they?
+
+The Historians can't agree on which group made the mistakes or how to read most of the Chief's handwriting, but in the commotion you notice an interesting detail: a lot of location IDs appear in both lists! Maybe the other numbers aren't location IDs at all but rather misinterpreted handwriting.
+
+This time, you'll need to figure out exactly how often each number from the left list appears in the right list. Calculate a total similarity score by adding up each number in the left list after multiplying it by the number of times that number appears in the right list.
+
+Here are the same example lists again:
+
+
+#+begin_example
+3   4
+4   3
+2   5
+1   3
+3   9
+3   3
+#+end_example
+
+For these example lists, here is the process of finding the similarity score:
+
++ The first number in the left list is 3. It appears in the right list three times, so the similarity score increases by 3 * 3 = 9.
++ The second number in the left list is 4. It appears in the right list once, so the similarity score increases by 4 * 1 = 4.
++ The third number in the left list is 2. It does not appear in the right list, so the similarity score does not increase (2 * 0 = 0).
++ The fourth number, 1, also does not appear in the right list.
++ The fifth number, 3, appears in the right list three times; the similarity score increases by 9.
++ The last number, 3, appears in the right list three times; the similarity score again increases by 9.
+
+So, for these example lists, the similarity score at the end of this process is 31 (9 + 4 + 0 + 0 + 9 + 9).

days/day1/day1.go

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+package day1
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"slices"
+	"strconv"
+	"strings"
+)
+
+func getDistance(x, y int) int {
+	// Take the distance between two numbers.
+	// The distance is the difference between the two numbers.
+
+	if x > y {
+		return (x - y)
+
+	} else {
+		return (y - x)
+
+	}
+}
+
+func processLine(line string) (int, int, error) {
+	// Split the line into fields.
+	fields := strings.Fields(line)
+	if len(fields) != 2 {
+		return 0, 0, fmt.Errorf("Expected 2 fields, got %d", len(fields))
+	}
+	num1, err := strconv.Atoi(fields[0])
+	if err != nil {
+		return 0, 0, fmt.Errorf("Failed to parse first number: %w", err)
+	}
+
+	num2, err := strconv.Atoi(fields[1])
+	if err != nil {
+		return 0, 0, fmt.Errorf("Failed to parse the second number: %w", err)
+	}
+
+	return num1, num2, nil
+
+}
+
+func readDataSet(filename string) ([]int, []int, error) {
+	file, err := os.Open(filename)
+	if err != nil {
+		return nil, nil, err
+	}
+	defer file.Close()
+
+	var firstSet, secondSet []int
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := scanner.Text()
+		num1, num2, err := processLine(line)
+		if err != nil {
+			return nil, nil, err
+		}
+		firstSet = append(firstSet, num1)
+		secondSet = append(secondSet, num2)
+	}
+
+	return firstSet, secondSet, nil
+}
+
+func numFreq(dataset []int) map[int]int {
+	// Take a slice of numbers and return an array of each number and the amount of times it occurs.
+	distribution := make(map[int]int)
+	for _, num := range dataset {
+		elem, ok := distribution[num]
+		if ok {
+			distribution[num] = elem + 1
+		} else {
+			distribution[num] = 1
+		}
+	}
+	return distribution
+}
+
+func partTwo(filename string) (int, error) {
+	//Solve part two.
+	var similarities int
+	firstSet, secondSet, err := readDataSet(filename)
+
+	if err != nil {
+		return 0, err
+	}
+
+	secondDistribution := numFreq(secondSet)
+
+	for _, num := range firstSet {
+		freq, ok := secondDistribution[num]
+		if ok {
+			similarity := num * freq
+			similarities = similarities + similarity
+		}
+	}
+
+	return similarities, nil
+}
+
+func partOne(filename string) (int, error) {
+	// Solve part one.
+
+	firstSet, secondSet, err := readDataSet(filename)
+
+	if err != nil {
+		return 0, err
+	}
+	slices.Sort(firstSet)
+	slices.Sort(secondSet)
+	if len(firstSet) != len(secondSet) {
+		return 0, fmt.Errorf("Error: Datasets are not the same size. %v != %v", len(firstSet), len(secondSet))
+	}
+	var distances int
+	for i := 0; i < len(firstSet); i++ {
+		distance := getDistance(firstSet[i], secondSet[i])
+		distances = distances + distance
+	}
+
+	return distances, nil
+}
+
+func Day1(filename string) {
+	distances, err := partOne(filename)
+	if err != nil {
+		fmt.Printf("Error: %v", err)
+		os.Exit(1)
+	}
+	fmt.Println("-------- PART 1 -------")
+	fmt.Printf("The total distance is %v\n", distances)
+	similarities, err := partTwo(filename)
+	if err != nil {
+		fmt.Printf("Error: %v", err)
+		os.Exit(1)
+	}
+
+	fmt.Println("-------- PART 2 -------")
+	fmt.Printf("The similarities between the two sets: %v\n", similarities)
+}

days/day1/day1_test.go

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+package day1
+
+import "testing"
+
+func Test_partTwo(t *testing.T) {
+	type args struct {
+		filename string
+	}
+	tests := []struct {
+		name    string
+		args    args
+		want    int
+		wantErr bool
+	}{
+		{
+			name:    "Example Part 2",
+			args:    args{filename: "example.txt"},
+			want:    31,
+			wantErr: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := partTwo(tt.args.filename)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("partTwo() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if got != tt.want {
+				t.Errorf("partTwo() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func Test_partOne(t *testing.T) {
+	type args struct {
+		filename string
+	}
+	tests := []struct {
+		name    string
+		args    args
+		want    int
+		wantErr bool
+	}{
+		{
+			name:    "Example Part 1",
+			args:    args{filename: "example.txt"},
+			want:    11,
+			wantErr: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := partOne(tt.args.filename)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("partOne() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if got != tt.want {
+				t.Errorf("partOne() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}

days/day1/example.txt

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+3   4
+4   3
+2   5
+1   3
+3   9
+3   3

go.mod

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+module git.eising.cloud/Eising/aoc2024
+
+go 1.23.1

main.go

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+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+
+	"git.eising.cloud/Eising/aoc2024/days/day1"
+)
+
+func main() {
+	day := flag.Int("day", 1, "Day of the challenge to run (1-24)")
+	useExample := flag.Bool("exampledata", false, "Load example data instead of actual challenge data.")
+
+	flag.Parse()
+
+	filename := fmt.Sprintf("days/day%d/test_input.txt", *day)
+
+	if *useExample {
+		filename = fmt.Sprintf("days/day%d/example.txt", *day)
+	}
+
+	if *day < 1 || *day > 24 {
+		fmt.Println("That's not very Christmas.")
+		os.Exit(1)
+	}
+
+	switch *day {
+	case 1:
+		day1.Day1(filename)
+	default:
+		fmt.Printf("Solution for day %d is not ready yet.\n", *day)
+	}
+
+}