AdventOfCode2021/14/main.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"strings"
	"time"
)

func main() {
	start := time.Now()
	partOne()
	duration := time.Since(start)
	partTwo()
	duration2 := time.Since(start)
	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
}

func makeScanner(test bool) *bufio.Scanner {
	var f *os.File
	if test {
		f, _ = os.Open("inputs/testinput")
	} else {
		f, _ = os.Open("inputs/input")
	}
	reader := bufio.NewReader(f)
	return bufio.NewScanner(reader)
}

func partOne() {
	scanner := makeScanner(false)

	polymer := map[string]int{}

	// initial state
	scanner.Scan()
	initial := scanner.Text()
	for i := 0; i < len(initial)-1; i++ {
		pair := string(initial[i]) + string(initial[i+1])
		polymer[pair]++
	}

	// eat empty line
	scanner.Scan()

	// parse rules
	rulemap := map[string][]string{}
	for scanner.Scan() {
		rule := strings.Split(scanner.Text(), " -> ")
		rulemap[rule[0]] = []string{
			string(rule[0][0]) + rule[1],
			rule[1] + string(rule[0][1]),
		}
	}

	// apply rules
	for i := 0; i < 10; i++ {
		newPolymer := map[string]int{}
		for p, c := range polymer {
			newPolymer[rulemap[p][0]] += c
			newPolymer[rulemap[p][1]] += c
		}
		polymer = newPolymer
	}

	// count elements
	count := map[string]int{}
	for p, c := range polymer {
		count[string(p[0])] += c
		count[string(p[1])] += c
	}

	// find max and min
	max, min := 0, 0
	for _, c := range count {
		if c > max {
			max = c
		}
		if c < min || min == 0 {
			min = c
		}
	}

	// handle rounding
	if (max-min)%2 == 1 {
		fmt.Println((max-min)/2 + 1)
	} else {
		fmt.Println((max - min) / 2)
	}
}

func partTwo() {
	scanner := makeScanner(false)

	polymer := map[string]int{}

	// initial state
	scanner.Scan()
	initial := scanner.Text()
	for i := 0; i < len(initial)-1; i++ {
		pair := string(initial[i]) + string(initial[i+1])
		polymer[pair]++
	}

	// eat empty line
	scanner.Scan()

	// parse rules
	rulemap := map[string][]string{}
	for scanner.Scan() {
		rule := strings.Split(scanner.Text(), " -> ")
		rulemap[rule[0]] = []string{
			string(rule[0][0]) + rule[1],
			rule[1] + string(rule[0][1]),
		}
	}

	// apply rules
	for i := 0; i < 40; i++ {
		newPolymer := map[string]int{}
		for p, c := range polymer {
			newPolymer[rulemap[p][0]] += c
			newPolymer[rulemap[p][1]] += c
		}
		polymer = newPolymer
	}

	// count elements
	count := map[string]int{}
	for p, c := range polymer {
		count[string(p[0])] += c
		count[string(p[1])] += c
	}

	// find max and min
	max, min := 0, 0
	for _, c := range count {
		if c > max {
			max = c
		}
		if c < min || min == 0 {
			min = c
		}
	}

	// handle rounding
	if (max-min)%2 == 1 {
		fmt.Println((max-min)/2 + 1)
	} else {
		fmt.Println((max - min) / 2)
	}
}