Advent of Code, 2022, Day 4

advent04.go

package main

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

type Iter[T any] func(func(T) bool) bool

func ScanText(s *bufio.Scanner) Iter[string] {
	return func(yield func(string) bool) bool {
		for s.Scan() {
			if !yield(s.Text()) {
				break
			}
		}
		return false
	}
}

func Lines(r io.Reader, err *error) Iter[string] {
	s := bufio.NewScanner(r)
	return func(yield func(string) bool) bool {
		ScanText(s)(yield)
		*err = s.Err()
		return false
	}
}

func parse(str string) (start, end int) {
	s, e, _ := strings.Cut(str, "-")
	sn, _ := strconv.ParseInt(s, 10, 0)
	en, _ := strconv.ParseInt(e, 10, 0)
	return int(sn), int(en)
}

func check(line string) bool {
	left, right, _ := strings.Cut(line, ",")
	l1, l2 := parse(left)
	r1, r2 := parse(right)

	return ((l1 >= r1) && (l2 <= r2)) || ((r1 >= l1) && (r2 <= l2))
}

func main() {
	file, err := os.Open("input.txt")
	if err != nil {
		panic(err)
	}
	defer file.Close()

	var total int
	for line := range Lines(file, &err) {
		if check(line) {
			total++
		}
	}
	if err != nil {
		panic(err)
	}

	fmt.Println(total)
}

go.mod

module advent04

go 1.21