adventofcode2023/day03.go

package main

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

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

type enginepart struct {
	value int
	pos   int
	raw   string
}

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

outer:
	for pos := 0; ; pos++ {
		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) {
					value, _ := strconv.Atoi(string(b))
					for range b {
						parts = append(parts, enginepart{value: value, pos: pos, raw: string(b)})
					}
					pos += len(b) - 1

					if err == io.EOF {
						return parts
					}

					buf.UnreadByte()
					continue outer
				}

				b = append(b, digit)
			}

		} else if head != '.' {
			// head is a symbol
			parts = append(parts, enginepart{value: -1, pos: pos, raw: string(head)})

		} else {
			// head is a '.'
			parts = append(parts, enginepart{value: 0, pos: pos, raw: string(head)})
		}
	}
}

type day03 struct{}

func (d day03) solve1(r io.Reader) string {
	sum := 0
	parts := make([][]enginepart, 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 row := range parts {
		for item := range parts[row] {
			if sym := parts[row][item]; sym.value == -1 {

				for i := -1; i < 2; i++ {
					for j := -1; j < 2; {
						x := row + i
						y := item + j

						if x >= 0 && y >= 0 && x < len(parts) && y < len(parts[row]) {
							part := parts[x][y]
							if part.value > 0 {
								sum += part.value
								j += (part.pos + len(part.raw) - y)
							} else {
								j++
							}
						}

					}
				}
			}
		}
	}

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

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