aoc21/05/main.go

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"regexp"
	"strconv"
)

type Point struct {
	x int
	y int
}

type Line struct {
	start Point
	end   Point
}

func createLine(s []string) *Line {
	l := &Line{start: Point{}, end: Point{}}
	l.start.x, _ = strconv.Atoi(s[0])
	l.start.y, _ = strconv.Atoi(s[1])
	l.end.x, _ = strconv.Atoi(s[2])
	l.end.y, _ = strconv.Atoi(s[3])
	return l
}

func (l *Line) Walk() (p []Point, isDiagonal bool) {
	xstart, xend := minMax(l.start.x, l.end.x)
	ystart, yend := minMax(l.start.y, l.end.y)
	// diagonal line
	if xend-xstart == yend-ystart {
		isDiagonal = true
		for x, y := l.start.x, l.start.y; ; {
			p = append(p, Point{x: x, y: y})
			if x == l.end.x {
				break
			}
			if x > l.end.x {
				x--
			} else {
				x++
			}
			if y > l.end.y {
				y--
			} else {
				y++
			}
		}
		fmt.Print()
	} else {
		// horizontal line
		for x := xstart; x <= xend && l.start.y == l.end.y; x++ {
			p = append(p, Point{x: x, y: l.start.y})
		}
		// vertical line
		for y := ystart; y <= yend && l.start.x == l.end.x; y++ {
			p = append(p, Point{x: l.start.x, y: y})
		}
	}
	return
}

func minMax(a int, b int) (min int, max int) {
	if a > b {
		min, max = b, a
	} else {
		min, max = a, b
	}
	return
}

func main() {
	file, err := os.Open("input.txt")
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)
	scanner.Split(bufio.ScanLines)

	r := regexp.MustCompile("[0-9]+")

	floorMap := make(map[Point]int)
	var overlapCount int
	diags := make([]Point, 0)

	for scanner.Scan() {
		text := scanner.Text()
		coords := r.FindAllString(text, -1)
		line := createLine(coords)
		points, isDiagonal := line.Walk()

		if isDiagonal {
			diags = append(diags, points...)
			continue
		}

		for _, p := range points {
			if floorMap[p] == 1 {
				overlapCount++
			}
			floorMap[p]++
		}
	}

	fmt.Println("Part one: ", overlapCount)

	for _, p := range diags {
		if floorMap[p] == 1 {
			overlapCount++
		}
		floorMap[p]++
	}

	fmt.Println("Part two: ", overlapCount)
}