aoc2023/day-3/one.go

package main

import (
	"fmt"
	"strconv"
	"unicode"
)

var symbols = [][]bool{}

// enginePart represents a single engine part
type enginePart struct {
	digits []digit
}

// realValue returns the numeric value of all digits combined
func (e *enginePart) realValue() (int, error) {
	var numStr string
	for _, digit := range e.digits {
		numStr += fmt.Sprintf("%d", digit.raw)
	}
	n, err := strconv.Atoi(numStr)
	if err != nil {
		return 0, err
	}
	return n, nil
}

// digit represents a single digit in an engine part
type digit struct {
	row  int
	col  int
	raw  int
	pass bool
}

// checkDigit checks if any neighbouring characters are true (in symbol matrix)
func checkDigit(d digit) digit {
	i := d.col - 1
	for ; i < len(symbols[d.row]) && i <= d.col+1; i += 1 {
		if i < 0 {
			continue
		}
		if d.row != 0 {
			if symbols[d.row-1][i] {
				d.pass = true
				break
			}
		}
		if symbols[d.row][i] {
			d.pass = true
			break
		}
		if d.row != len(symbols)-1 {
			if symbols[d.row+1][i] {
				d.pass = true
				break
			}
		}
	}
	return d
}

// checkDigits runs each digit in an engine part through checkDigit()
func checkDigits(i, j int, line string) (int, int, error) {
	enginePart := enginePart{}
	for ; j < len(line); j += 1 {
		if !unicode.IsNumber(rune(line[j])) {
			break
		}
		enginePart.digits = append(enginePart.digits, checkDigit(digit{row: i, col: j, raw: int(line[j]) - '0', pass: false}))
	}

	if anyTrue(enginePart.digits) {
		engineParts[i] = append(engineParts[i], enginePart)
		n, err := enginePart.realValue()
		if err != nil {
			return 0, 0, err
		}
		return j, n, nil
	}
	return j, 0, nil
}

// symbolToBool generates a boolean matrix that represents the placement of symbols
func symbolToBool(line string) []bool {
	bool_arr := []bool{}
	for _, c := range line {
		bool_arr = append(bool_arr, !(unicode.IsNumber(c) || c == '.'))
	}
	return bool_arr
}

// one deciphers which numbers represent engine parts
// it returns the sum of all engine parts
func one(lines []string) (int, error) {
	for _, line := range lines {
		symbols = append(symbols, symbolToBool(line))
	}
	engineParts = make([][]enginePart, len(lines))

	sum := 0
	for i, line := range lines {
		for j := 0; j < len(line); j += 1 {
			if unicode.IsNumber(rune(line[j])) {
				next, n, err := checkDigits(i, j, line)
				if err != nil {
					return 0, err
				}
				sum += n
				j = next
			}
		}
	}

	return sum, nil
}