adventofcode2023/day03.go

package main

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

func isdigit(b byte) bool {
	return b >= 48 && b <= 57
}

func engineparts(buf *bufio.Reader) []int {
	parts := make([]int, 0, 150)

outer:
	for {
		head, err := buf.ReadByte()
		if err != nil {
			return parts
		}

		if isdigit(head) {
			// start recording digits
			b := make([]byte, 0, 10)
			b = append(b, head)

			// continue reading until number is exhausted
			for {
				digit, err := buf.ReadByte()
				if !isdigit(digit) || err == io.EOF {
					value, _ := strconv.Atoi(string(b))
					for range b {
						parts = append(parts, value)
					}

					buf.UnreadByte()
					continue outer
				}

				b = append(b, digit)
			}

		} else if head != '.' {
			// head is a symbol
			parts = append(parts, -1)

		} else {
			// head is a '.'
			parts = append(parts, 0)
		}
	}
}

type day03 struct{}

func (d day03) solve1(r io.Reader) string {
	sum := 0
	parts := make([][]int, 0, 100)
	scanner := bufio.NewScanner(r)

	for scanner.Scan() {
		line := scanner.Text()
		buf := bufio.NewReader(strings.NewReader(line))
		lineparts := engineparts(buf)
		parts = append(parts, lineparts)
	}

	for i := 1; i < len(parts)-1; i++ {
		for j := 1; j < len(parts[i])-1; j++ {
			cursor := parts[i][j]
			if cursor == -1 {
			row:
				for i2 := -1; i2 <= 1; i2++ {
					for j2 := -1; j2 <= 1; j2++ {
						val := parts[i+i2][j+j2]
						if val > 0 {
							sum += val
							continue row
						}
					}
				}
			}
		}
	}

	return fmt.Sprintf("%d", sum)
}

func (d day03) solve2(r io.Reader) string {
	return ""
}