advent2024/day5/main.go

package main

import (
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	if len(os.Args) < 2 {
		panic("Provide input file")
	}
	inputFile := os.Args[1]

	part1, part2 := solution(inputFile)
	fmt.Printf("(%s) Part 1: %d\n(%s) Part 2: %d\n", inputFile, part1, inputFile, part2)
}

type Rule struct {
	Left  int
	Right int
}

func solution(inputFile string) (int, int) {
	input, err := os.Open(inputFile)
	if err != nil {
		panic(err)
	}
	defer input.Close()

	var rules []Rule
	for {
		var x, y int
		_, err := fmt.Fscanf(input, "%d|%d\n", &x, &y)
		if err != nil {
			break
		}
		rules = append(rules, Rule{Left: x, Right: y})
	}

	// for _, rule := range rules {
	// 	fmt.Printf("%d|%d\n", rule.Left, rule.Right)
	// }

	// checking if the updates are correct
	var validSum, invalidSum int
	for {
		var numStr string
		_, err := fmt.Fscanf(input, "%s\n", &numStr)
		if err != nil {
			break
		}
		parts := strings.Split(numStr, ",")
		updatePages := make([]int, 0)
		for _, part := range parts {
			partInt, _ := strconv.Atoi(part)
			updatePages = append(updatePages, partInt)
		}

		validUpdate := true
		for curr := 0; curr < len(updatePages); curr++ {
			for check := 0; check < len(updatePages); check++ {
				if curr == check {
					continue
				}
				if curr < check {
					valid := isValid(rules, updatePages[curr], updatePages[check])
					if !valid {
						fmt.Printf("Invalid %v\n", updatePages)
						validUpdate = false
						break
					}
				} else {
					valid := isValid(rules, updatePages[check], updatePages[curr])
					if !valid {
						fmt.Printf("Invalid %v\n", updatePages)
						validUpdate = false
					}
				}
			}
			if !validUpdate {
				break
			}
		}

		if validUpdate {
			validSum += updatePages[len(updatePages)/2]
		} else {
			invalidSum += reorderedMid(updatePages, rules)
		}
	}
	return validSum, invalidSum
}

func reorderedMid(pages []int, rules []Rule) int {
	corrected := false
	for !corrected {
		for i := 0; i < len(pages); i++ {
			for j := 1; j < len(pages); j++ {
				if i == j {
					continue
				}
				if i < j {
					valid := isValid(rules, pages[i], pages[j])
					if !valid {
						pages[i], pages[j] = pages[j], pages[i]
					}
				} else {
					valid := isValid(rules, pages[j], pages[i])
					if !valid {
						pages[i], pages[j] = pages[j], pages[i]
					}
				}
			}
		}

		corrected = wasCorrected(pages, rules)
	}
	fmt.Printf("Corrected %v\n", pages)
	return pages[len(pages)/2]
}

func wasCorrected(pages []int, rules []Rule) bool {
	for i := 0; i < len(pages); i++ {
		for j := 1; j < len(pages); j++ {
			if i == j {
				continue
			}
			if i < j {
				valid := isValid(rules, pages[i], pages[j])
				if !valid {
					return false
				}
			} else {
				valid := isValid(rules, pages[j], pages[i])
				if !valid {
					return false
				}
			}
		}
	}
	return true
}

func isValid(rules []Rule, left, right int) bool {
	for _, rule := range rules {
		if rule.Left == right && rule.Right == left {
			return false
		}
	}
	return true
}