adventofcode/2024/day05/main.go

package main

import (
	"errors"
	"fmt"
	"strings"

	helpers "git.bullercodeworks.com/brian/adventofcode/helpers"
)

func main() {
	inp := helpers.StdinToStringSlice()
	part1(inp)
	fmt.Println()
	part2(inp)
}

func part1(inp []string) {
	rules, updates := processInput(inp)
	var result int
	for i := range updates {
		if rules.Validate(updates[i]) {
			result = result + updates[i][len(updates[i])/2]
		}
	}
	fmt.Println("# Part 1")
	fmt.Printf("Valid Updates: %d\n", result)
}

func part2(inp []string) {
	rules, updates := processInput(inp)
	var result int
	for i := range updates {
		var iter int
		var wasIncorrect bool
		for !rules.Validate(updates[i]) {
			if iter > 100 {
				panic(errors.New("Naive correction won't work..."))
			}
			updates[i] = rules.Correct(updates[i])
			iter++
			wasIncorrect = true
		}
		if wasIncorrect {
			result = result + updates[i][len(updates[i])/2]
		}
	}
	fmt.Println("# Part 2")
	fmt.Printf("Corrected Updates: %d\n", result)
}

func processInput(inp []string) (*PageOrderingRules, [][]int) {
	var rawRules []string
	var strUpdates []string
	var inRules bool
	inRules = true
	for i := range inp {
		if inp[i] == "" {
			inRules = false
			continue
		}
		if inRules {
			rawRules = append(rawRules, inp[i])
		} else {
			strUpdates = append(strUpdates, inp[i])
		}
	}
	var updates [][]int
	rules := PageOrderingRules{Rules: parseOrderingRules(rawRules)}
	for i := range strUpdates {
		updates = append(updates, parseUpdate(strUpdates[i]))
	}

	return &rules, updates
}

type PageOrderingRules struct {
	Rules []Rule
}

func (p *PageOrderingRules) Correct(update []int) []int {
	if p.Validate(update) {
		return update
	}
	for i := range p.Rules {
		update = p.Rules[i].Correct(update)
	}
	return update
}

func (p *PageOrderingRules) Validate(update []int) bool {
	for i := range p.Rules {
		if !p.Rules[i].Validates(update) {
			return false
		}
	}
	return true
}

func (p PageOrderingRules) String() string {
	var ret string
	for i := range p.Rules {
		ret = fmt.Sprintf("%s%s\n", ret, p.Rules[i])
	}
	return ret
}

type Rule struct {
	first, second int
}

func (r *Rule) Validates(update []int) bool {
	for i := range update {
		if update[i] == r.first {
			for j := range update {
				if update[j] == r.second {
					return i < j
				}
			}
		}
	}
	return true
}

func (r *Rule) Correct(update []int) []int {
	if r.Validates(update) {
		return update
	}
	var idx, jdx int
	for i := range update {
		if update[i] == r.first {
			idx = i
		}
		if update[i] == r.second {
			jdx = i
		}
	}
	update[idx], update[jdx] = update[jdx], update[idx]
	return update
}

func (r Rule) String() string {
	return fmt.Sprintf("%d|%d", r.first, r.second)
}

func parseOrderingRules(inp []string) []Rule {
	var ret []Rule
	for i := range inp {
		if inp[i] == "" {
			return ret
		}
		rule := Rule{}
		fmt.Sscanf(inp[i], "%d|%d", &rule.first, &rule.second)
		ret = append(ret, rule)
	}
	return ret
}

func parseUpdate(inp string) []int {
	var ret []int
	pts := strings.Split(inp, ",")
	for i := range pts {
		var wrk int
		fmt.Sscanf(pts[i], "%d", &wrk)
		ret = append(ret, wrk)
	}
	return ret
}