Day 5 finished

2024/day5/main.go

@@ -0,0 +1,194 @@
+package main
+
+import (
+	"bufio"
+	"flag"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func reorderPages(rules [][]int, update []int) []int {
+	dependents := make(map[int][]int)
+	dependencies := make(map[int]int)
+
+	inUpdate := make(map[int]bool)
+	for _, num := range update {
+		inUpdate[num] = true
+	}
+
+	for _, rule := range rules {
+		pageA, pageB := rule[0], rule[1]
+		if !inUpdate[pageA] || !inUpdate[pageB] {
+			continue
+		}
+
+		dependents[pageA] = append(dependents[pageA], pageB)
+		dependencies[pageB]++
+	}
+
+	ordered := []int{}
+	queue := []int{}
+
+	for _, num := range update {
+		if dependencies[num] == 0 {
+			queue = append(queue, num)
+		}
+	}
+
+	// Process the queue
+	for len(queue) > 0 {
+		page := queue[0]
+		queue = queue[1:]
+		ordered = append(ordered, page)
+
+		for _, dependent := range dependents[page] {
+			dependencies[dependent]--
+			if dependencies[dependent] == 0 {
+				queue = append(queue, dependent)
+			}
+		}
+	}
+
+	pageSeen := make(map[int]bool)
+	for _, page := range ordered {
+		pageSeen[page] = true
+	}
+	for _, page := range update {
+		if !pageSeen[page] {
+			ordered = append(ordered, page)
+		}
+	}
+
+	return ordered
+}
+
+func Part1(rules, updates [][]int) int {
+	middleSum := 0
+
+	for _, update := range updates {
+		pageIndex := make(map[int]int)
+		for i, num := range update {
+			pageIndex[num] = i
+		}
+
+		failed := false
+		for _, rule := range rules {
+			pageA, pageB := rule[0], rule[1]
+
+			indexA, existsA := pageIndex[pageA]
+			indexB, existsB := pageIndex[pageB]
+
+			if existsA && existsB && indexA > indexB {
+				failed = true
+				break
+			}
+		}
+
+		if failed {
+			continue
+		}
+
+		middleSum += update[len(update)/2]
+	}
+
+	return middleSum
+}
+
+func Part2(rules, updates [][]int) int {
+	middleSum := 0
+
+	for _, update := range updates {
+		pageIndex := make(map[int]int)
+		for i, num := range update {
+			pageIndex[num] = i
+		}
+
+		failed := false
+		for _, rule := range rules {
+			pageA, pageB := rule[0], rule[1]
+
+			indexA, existsA := pageIndex[pageA]
+			indexB, existsB := pageIndex[pageB]
+
+			if existsA && existsB && indexA > indexB {
+				failed = true
+				break
+			}
+		}
+
+		if !failed {
+			continue
+		}
+
+		fixedUpdate := reorderPages(rules, update)
+
+		middleSum += fixedUpdate[len(fixedUpdate)/2]
+	}
+
+	return middleSum
+}
+
+func main() {
+	flag.Parse()
+
+	if len(flag.Args()) == 0 {
+		panic("Please provide a filename")
+	}
+
+	filename := flag.Args()[0]
+
+	file, err := os.Open(filename)
+	if err != nil {
+		panic(err)
+	}
+	defer file.Close()
+
+	var rules [][]int
+	var updates [][]int
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		if line == "" {
+			continue
+		}
+
+		nums := strings.Split(line, "|")
+		if len(nums) == 2 {
+			rule := make([]int, 2)
+			for i, num := range nums {
+				rule[i], err = strconv.Atoi(num)
+				if err != nil {
+					panic(err)
+				}
+			}
+
+			rules = append(rules, rule)
+		} else {
+			nums := strings.Split(line, ",")
+			update := []int{}
+			for _, num := range nums {
+				parsedNum, err := strconv.Atoi(num)
+				if err != nil {
+					panic(err)
+				}
+
+				update = append(update, parsedNum)
+			}
+
+			updates = append(updates, update)
+		}
+	}
+
+	if err := scanner.Err(); err != nil {
+		panic(err)
+	}
+
+	answer := Part1(rules, updates)
+	fmt.Println(answer)
+
+	answer = Part2(rules, updates)
+	fmt.Println(answer)
+}