aoc2023/day-18/one.go

package main

import (
	"math"
	"regexp"
)

var r = regexp.MustCompile(`(?P<direction>[A-Z]) (?P<count>[0-9]+) \((?P<colour>.*)\)`)

func fromRegex(imager *imager, lines []string) {
	for _, line := range lines {
		direction, count := func() (string, int) {
			x := getParams(r, line)
			return x["direction"], mustConv(x["count"])
		}()
		imager.add(direction, count)
	}
}

func buildImage(withParser func(imager *imager, lines []string), imager *imager, lines []string) {
	withParser(imager, lines)
}

// one returns the area of the polygon described by imager.space
func one(lines []string) int {
	imager := newImager()
	buildImage(fromRegex, imager, lines)

	area := 0
	for i := 0; i < len(imager.space); i++ {
		next := imager.space[(i+1)%len(imager.space)]
		area += imager.space[i].X*next.Y - imager.space[i].Y*next.X
	}

	// add perimeter to area within perimeter
	area = len(imager.space) + (int(math.Abs(float64(area))) / 2)

	return area - len(imager.space)/2 + 1
}