package main

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

func IntAbs(a int) int {
	if a >= 0 {
		return a
	}
	return -a
}

func main() {
	part2(readData("data.txt"))
}

func readData(fileName string) (list1, list2 []int) {
	fp, err := os.Open(fileName)
	if err != nil {
		panic(err)
	}

	scanner := bufio.NewScanner(fp)

	list1 = make([]int, 0)
	list2 = make([]int, 0)

	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())
		split := strings.Split(line, "   ")
		if len(split) != 2 {
			continue
		}

		value1, err := strconv.Atoi(split[0])
		if err != nil {
			continue
		}

		value2, err := strconv.Atoi(split[1])
		if err != nil {
			continue
		}

		list1 = append(list1, value1)
		list2 = append(list2, value2)
	}

	return
}

func part1(list1, list2 []int) {
	sort.Sort(sort.IntSlice(list1))
	sort.Sort(sort.IntSlice(list2))

	dist := 0
	for i := range list1 {
		dist += IntAbs(list1[i] - list2[i])
	}

	fmt.Println(dist)
}

func countInstances(list []int) (counts map[int]int) {
	counts = make(map[int]int)
	for _, n := range list {
		counts[n] += 1
	}
	return
}

func part2(list1, list2 []int) {
	counts1 := countInstances(list1)
	counts2 := countInstances(list2)

	total := 0
	for n, c1 := range counts1 {
		c2, _ := counts2[n]
		total += n * c1 * c2
	}

	fmt.Println(total)
}