Day 5

day5/example.txt

@@ -0,0 +1,28 @@
+47|53
+97|13
+97|61
+97|47
+75|29
+61|13
+75|53
+29|13
+97|29
+53|29
+61|53
+97|53
+61|29
+47|13
+75|47
+97|75
+47|61
+75|61
+47|29
+75|13
+53|13
+
+75,47,61,53,29
+97,61,53,29,13
+75,29,13
+75,97,47,61,53
+61,13,29
+97,13,75,29,47

day5/go.mod

@@ -0,0 +1,3 @@
+module stevenlr.com/aoc2024/day5
+
+go 1.22.2

day5/main.go

@@ -0,0 +1,113 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"slices"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+func main() {
+	fmt.Println(doTheThing("example.txt"))
+	fmt.Println(doTheThing("data.txt"))
+}
+
+func fill[T any](s []T, value T) {
+	for i := range s {
+		s[i] = value
+	}
+}
+
+func doTheThing(fileName string) (resultPart1, resultPart2 int) {
+	fp, err := os.Open(fileName)
+	if err != nil {
+		panic(err)
+	}
+
+	scanner := bufio.NewScanner(fp)
+	forbiddenAfter := readForbiddenAfter(scanner)
+	seen := make([]bool, 100)
+	forbidden := make([]bool, 100)
+
+	for scanner.Scan() {
+		seq := readLine(strings.TrimSpace(scanner.Text()))
+		fill(seen, false)
+		fill(forbidden, false)
+
+		ok := true
+
+		for _, n := range seq {
+			if seen[n] {
+				continue
+			}
+
+			if forbidden[n] {
+				ok = false
+				break
+			}
+
+			for _, f := range forbiddenAfter[n] {
+				forbidden[f] = true
+			}
+
+			seen[n] = true
+		}
+
+		if ok {
+			resultPart1 += seq[len(seq)/2]
+		} else {
+			sort.Slice(seq, func(i, j int) bool {
+				return slices.Index(forbiddenAfter[seq[j]], seq[i]) != -1
+			})
+			resultPart2 += seq[len(seq)/2]
+		}
+	}
+
+	return
+}
+
+func readLine(s string) (line []int) {
+	split := strings.Split(s, ",")
+	line = make([]int, len(split))
+	for i, num := range split {
+		n, err := strconv.Atoi(num)
+		if err != nil {
+			panic(err)
+		}
+		line[i] = n
+	}
+	return
+}
+
+func readForbiddenAfter(scanner *bufio.Scanner) (forbiddenAfter map[int][]int) {
+	forbiddenAfter = make(map[int][]int)
+
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if len(line) == 0 {
+			return
+		}
+
+		split := strings.Split(line, "|")
+		if len(split) != 2 {
+			panic("Not enough data for ordering")
+		}
+
+		a, err := strconv.Atoi(split[0])
+		if err != nil {
+			panic(err)
+		}
+
+		b, err := strconv.Atoi(split[1])
+		if err != nil {
+			panic(err)
+		}
+
+		forbiddenAfter[b] = append(forbiddenAfter[b], a)
+	}
+
+	return
+}

go.work

@@ -5,4 +5,5 @@ use (
 	./day2
 	./day3
 	./day4
+	./day5
 )