aoc2023/day-3/two.go

package main

var engineParts [][]enginePart

// getGearRatio returns the product of engine parts if exactly two neighbour a gear
func getGearRatio(row, col int) (int, error) {
	partsConsidered := []enginePart{}

	i := row - 1
	for ; i < len(engineParts) && i <= row+1; i += 1 {
		if i < 0 {
			continue
		}
		for _, enginePart := range engineParts[i] {
			for _, digit := range enginePart.digits {
				if digit.pass && digit.col == col-1 || digit.col == col || digit.col == col+1 {
					partsConsidered = append(partsConsidered, enginePart)
					break
				}
			}
		}
	}
	if len(partsConsidered) == 2 {
		n1, err := partsConsidered[0].realValue()
		if err != nil {
			return 0, err
		}
		n2, err := partsConsidered[1].realValue()
		if err != nil {
			return 0, err
		}
		return n1 * n2, nil
	}
	return 0, nil
}

// two returns the sum of all gear ratios
func two(lines []string) (int, error) {
	sum := 0
	for i, line := range lines {
		for j, c := range line {
			if rune(c) == '*' {
				n, err := getGearRatio(i, j)
				if err != nil {
					return 0, err
				}
				sum += n
			}
		}
	}

	return sum, nil
}