aoc2023/day3/day3.go

package day3

import (
	"fmt"
	"strconv"
)

type Number struct {
	value int
	l     int
	js    int
	je    int
}

type Gear struct {
	l int
	c int
}

var gears map[Gear]*[]*Number

func parseNumber(lineNum int, line string, start int) *Number {
	js := start

	// move to first digit
	for ; js < len(line); js++ {

		c := line[js]

		if c >= '0' && c <= '9' {
			break
		}
	}

	// return nil if no digit
	if js == len(line) {
		return nil
	}

	je := js + 1

	// move to last digit in sequence
	for ; je < len(line); je++ {

		c := line[je]

		if c < '0' || c > '9' {
			break
		}
	}

	//fmt.Println("-->", js, je)
	num, err := strconv.Atoi(line[js:je])
	if err != nil {
		fmt.Println(err)
	}

	return &Number{
		value: num,
		l:     lineNum,
		js:    js,
		je:    je - 1,
	}
}

func hasGearInRange(lineNum int, line string, start int, end int) *Gear {
	i := start - 1
	if i < 1 {
		i = 0
	}

	for ; i < len(line) && i <= end+1; i++ {
		c := line[i]

		if (c < '0' || c > '9') && c != '.' {
			return &Gear{
				l: lineNum,
				c: i,
			}
		}
	}

	return nil
}

func hasAdjacentSymbol(n *Number, before string, line string, after string) *Gear {

	if before != "" {
		g := hasGearInRange(n.l-1, before, n.js, n.je)

		if g != nil {
			return g
		}
	}

	g := hasGearInRange(n.l, line, n.js, n.je)
	if g != nil {
		return g
	}

	if after != "" {
		g := hasGearInRange(n.l+1, after, n.js, n.je)

		if g != nil {
			return g
		}
	}

	return nil
}

func PartNumberSum(lines []string) int {
	result := 0

	for i, line := range lines {

		for j := 0; j < len(line); {
			num := parseNumber(i, line, j)

			if num == nil {
				break // no new number on this line
			}

			// number found
			before := ""
			after := ""

			if i > 0 {
				before = lines[i-1]
			}

			if i < len(lines)-1 {
				after = lines[i+1]
			}

			g := hasAdjacentSymbol(num, before, line, after)
			b := g != nil
			fmt.Printf("%t : Found %d at line %d between col %d and col %d\n", b, num.value, i, num.js, num.je)
			if b {
				result += num.value
			}

			// move cursor to the first char following the number
			j = num.je + 1
		}
	}

	return result
}

func markGearInRange(n *Number, lineNum int, line string, start int, end int) {
	i := start - 1
	if i < 1 {
		i = 0
	}

	for ; i < len(line) && i <= end+1; i++ {
		c := line[i]

		if (c < '0' || c > '9') && c != '.' {
			key := Gear{
				l: lineNum,
				c: i,
			}

			nums, ok := gears[key]
			if !ok {
				newNums := make([]*Number, 0)
				nums = &newNums
				gears[key] = nums
			}
			newNums := append(*nums, n)
			gears[key] = &newNums
		}
	}
}

func markAdjacentSymbols(n *Number, before string, line string, after string) {

	if before != "" {
		markGearInRange(n, n.l-1, before, n.js, n.je)
	}

	markGearInRange(n, n.l, line, n.js, n.je)

	if after != "" {
		markGearInRange(n, n.l+1, after, n.js, n.je)
	}
}

func GearRatioSum(lines []string) int64 {
	result := int64(0)
	gears = make(map[Gear]*[]*Number)

	for i, line := range lines {

		for j := 0; j < len(line); {
			num := parseNumber(i, line, j)

			if num == nil {
				break // no new number on this line
			}

			// number found
			before := ""
			after := ""

			if i > 0 {
				before = lines[i-1]
			}

			if i < len(lines)-1 {
				after = lines[i+1]
			}

			markAdjacentSymbols(num, before, line, after)

			// move cursor to the first char following the number
			j = num.je + 1
		}
	}

	for k, v := range gears {
		t := *v
		if len(t) == 2 {
			ratio := t[0].value * t[1].value
			fmt.Printf("Found gear at line %d and col %d with ratio %v\n", k.l, k.c, ratio)
			result += int64(ratio)
		}
	}
	return result
}