adventoc/2024/day01.go

package main

import (
	"bufio"
	"fmt"
	"io"
	"log"
	"os"
	"sort"
)

func part1(r io.Reader) string {
	s := bufio.NewScanner(r)
	var sum int
	var left, right []int

	var lft, rgh int
	for s.Scan() {
		fmt.Sscanf(s.Text(), "%d   %d", &lft, &rgh)
		left, right = append(left, lft), append(right, rgh)
	}

	sort.Ints(left)
	sort.Ints(right)

	for i := range right {
		sum += abs(left[i] - right[i])
	}

	return printi(sum)
}

func part2(r io.Reader) string {
	s := bufio.NewScanner(r)
	var sum int
	var left []int
	right := make(map[int]int)

	var lft, rgh int
	for s.Scan() {
		fmt.Sscanf(s.Text(), "%d   %d", &lft, &rgh)
		left = append(left, lft)
		right[rgh]++
	}

	sort.Ints(left)

	for i := range left {
		sum += left[i] * right[left[i]]
	}

	return printi(sum)
}

func main() {
	f, err := os.Open("day01.txt")
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()

	fmt.Println(part1(f))
	f.Seek(0, 0)
	fmt.Println(part2(f))
}