adventofcode/2023/day03/main.go

package main

import (
	"fmt"

	h "git.bullercodeworks.com/brian/adventofcode/helpers"
)

func main() {
	inp := h.StdinToStringSlice()
	part1(inp)
	part2(inp)
}

func part1(input []string) {
	bm := h.StringSliceToCoordByteMap(input)
	symbols := bm.FindAllNot('0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.')
	// Gather a list of numbers that are adjacent to the symbols
	nums := make(map[h.Coordinate]int)
	for k, _ := range symbols {
		wrk := findPartNumsFrom(bm, k)
		for coord, val := range wrk {
			nums[coord] = val
		}
	}
	var sum int
	for _, v := range nums {
		sum += v
	}
	fmt.Println("# Part 1")
	fmt.Println(sum)
}

func part2(input []string) {
	bm := h.StringSliceToCoordByteMap(input)
	maybeGears := bm.FindAll('*')
	var ratioSum int
	for _, k := range maybeGears {
		wrk := findPartNumsFrom(bm, k)
		if len(wrk) != 2 {
			// It's not a gear
			continue
		}
		var second bool
		var ratio int
		for _, v := range wrk {
			if !second {
				ratio += v
				second = true
			} else {
				ratio *= v
			}
		}
		ratioSum += ratio
	}
	fmt.Println("# Part 2")
	fmt.Println(ratioSum)
}

func findPartNumsFrom(m h.CoordByteMap, c h.Coordinate) map[h.Coordinate]int {
	partNums := make(map[h.Coordinate]int)
	for _, chk := range []h.Coordinate{
		c.North(),
		c.NE(),
		c.East(),
		c.SE(),
		c.South(),
		c.SW(),
		c.West(),
		c.NW(),
	} {
		if m.Get(chk) >= '0' && m.Get(chk) <= '9' {
			v, pos := parseNumAt(m, chk)
			partNums[pos] = v
		}
	}
	return partNums
}

// parseNumAt returns the number at c and the Coordinate
// that the first digit of that number is at
func parseNumAt(m h.CoordByteMap, c h.Coordinate) (int, h.Coordinate) {
	var resStr string
	startCoord := c
	// From 'c' move left until we find the first digit
	chk := m.Get(startCoord)
	for coordIsNum(m, startCoord) {
		startCoord = startCoord.West()
		chk = m.Get(startCoord)
	}
	startCoord = startCoord.East()

	// Now put the number at 'startCoord' together
	parseNum := startCoord
	chk = m.Get(startCoord)
	for coordIsNum(m, parseNum) {
		resStr = fmt.Sprintf("%s%s", resStr, string(chk))
		parseNum = parseNum.East()
		chk = m.Get(parseNum)
	}
	if resStr == "" {
		return -1, h.Coordinate{X: -1, Y: -1}
	}
	return h.Atoi(resStr), startCoord
}

func coordIsNum(m h.CoordByteMap, c h.Coordinate) bool {
	wrk := m.Get(c)
	return wrk >= '0' && wrk <= '9'
}