day 05 solution

solutions/alessio/day05/day05.go

@@ -0,0 +1,127 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func check(e error) {
+	if e != nil {
+		panic(e)
+	}
+}
+
+type PrecKey struct {
+	before int
+	after  int
+}
+
+func part1(lines []string) {
+	// see https://go.dev/blog/maps#key-types for more details about this implementation vs using a map of maps
+	prec := make(map[PrecKey]bool)
+	updatesLine := 0
+	for i, pair := range lines {
+		if pair == "" {
+			updatesLine = i + 1
+			break
+		}
+		var a, b int
+		fmt.Sscanf(pair, "%d|%d", &a, &b)
+		prec[PrecKey{a, b}] = true
+	}
+
+	sumMiddle := 0
+	for i := updatesLine; i < len(lines); i++ {
+		isValid := true
+		strs := strings.Split(lines[i], ",")
+		nums := make([]int, 0, len(strs))
+		for _, s := range strs {
+			n, _ := strconv.Atoi(s)
+			nums = append(nums, n)
+		}
+
+		for j := range len(nums) {
+			for k := j + 1; k < len(nums); k++ {
+				if (!prec[PrecKey{nums[j], nums[k]}]) {
+					isValid = false
+					break
+				}
+			}
+			if !isValid {
+				break
+			}
+		}
+
+		if isValid {
+			sumMiddle += nums[len(nums)/2]
+		}
+	}
+
+	fmt.Println(sumMiddle)
+}
+
+func part2(lines []string) {
+	prec := make(map[PrecKey]bool)
+	updatesLine := 0
+	for i, pair := range lines {
+		if pair == "" {
+			updatesLine = i + 1
+			break
+		}
+		var a, b int
+		fmt.Sscanf(pair, "%d|%d", &a, &b)
+		prec[PrecKey{a, b}] = true
+	}
+
+	sumMiddle := 0
+	for i := updatesLine; i < len(lines); i++ {
+		isValid := true
+		strs := strings.Split(lines[i], ",")
+		nums := make([]int, 0, len(strs))
+		for _, s := range strs {
+			n, _ := strconv.Atoi(s)
+			nums = append(nums, n)
+		}
+
+		for j := range len(nums) {
+			for k := j + 1; k < len(nums); k++ {
+				if (!prec[PrecKey{nums[j], nums[k]}]) {
+					isValid = false
+					break
+				}
+			}
+			if !isValid {
+				break
+			}
+		}
+
+		if !isValid {
+			correctNums := make([]int, 0, len(nums))
+			for j := range len(nums) {
+				correctNums = append(correctNums, nums[j])
+			}
+
+			for j := range len(nums) - 1 {
+				for k := range len(nums) - j - 1 {
+					if prec[PrecKey{correctNums[k+1], correctNums[k]}] {
+						correctNums[k], correctNums[k+1] = correctNums[k+1], correctNums[k]
+					}
+				}
+			}
+			sumMiddle += correctNums[len(correctNums)/2]
+		}
+	}
+
+	fmt.Println(sumMiddle)
+}
+func main() {
+	data, err := os.ReadFile("./input05.txt")
+	check(err)
+
+	lines := strings.Split(strings.Trim(string(data), "\r\n"), "\r\n")
+
+	part1(lines)
+	part2(lines)
+}

solutions/alessio/day05/go.mod

@@ -0,0 +1,3 @@
+module aoc4
+
+go 1.23.3