AdventOfCode2021/13/main.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"
)

func mustAtoi(line string) int {
	i, _ := strconv.Atoi(line)
	return i
}

func main() {
	start := time.Now()
	partOne()
	duration := time.Since(start)
	partTwo()
	duration2 := time.Since(start)
	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
}

func makeScanner(test bool) *bufio.Scanner {
	var f *os.File
	if test {
		f, _ = os.Open("inputs/testinput")
	} else {
		f, _ = os.Open("inputs/input")
	}
	reader := bufio.NewReader(f)
	return bufio.NewScanner(reader)
}

type point struct {
	x int
	y int
}

func partOne() {
	scanner := makeScanner(false)

	// parse points
	points := make(map[point]struct{}, 0)
	for scanner.Scan() {
		line := scanner.Text()
		if line == "" {
			break
		}
		p := strings.Split(line, ",")
		points[point{
			x: mustAtoi(p[0]),
			y: mustAtoi(p[1]),
		}] = struct{}{}
	}

	// make first fold
	scanner.Scan()
	f := strings.Split(scanner.Text(), "=")
	orientation := strings.Split(f[0], " ")[2]
	crease := mustAtoi(f[1])
	if orientation == "y" {
		for p := range points {
			if p.y > crease {
				delete(points, p)
				points[point{x: p.x, y: p.y - ((p.y - crease) * 2)}] = struct{}{}
			}
		}
	}
	if orientation == "x" {
		for p := range points {
			if p.x > crease {
				delete(points, p)
				points[point{x: p.x - ((p.x - crease) * 2), y: p.y}] = struct{}{}
			}
		}
	}
	fmt.Println(len(points))
}

func partTwo() {
	scanner := makeScanner(false)

	// parse points
	points := make(map[point]struct{}, 0)
	for scanner.Scan() {
		line := scanner.Text()
		if line == "" {
			break
		}
		p := strings.Split(line, ",")
		points[point{
			x: mustAtoi(p[0]),
			y: mustAtoi(p[1]),
		}] = struct{}{}
	}
	// do folds
	for scanner.Scan() {
		line := scanner.Text()
		f := strings.Split(line, "=")
		orientation := strings.Split(f[0], " ")[2]
		crease := mustAtoi(f[1])
		if orientation == "y" {
			for p := range points {
				if p.y > crease {
					delete(points, p)
					points[point{x: p.x, y: p.y - ((p.y - crease) * 2)}] = struct{}{}
				}
			}
		}
		if orientation == "x" {
			for p := range points {
				if p.x > crease {
					delete(points, p)
					points[point{x: p.x - ((p.x - crease) * 2), y: p.y}] = struct{}{}
				}
			}
		}
	}
	// print letters
	for y := 0; y < 6; y++ { // six units tall
		for x := 0; x < 5*8; x++ { // 5 units wide, 8 letters
			if _, ok := points[point{x: x, y: y}]; ok {
				fmt.Printf("#")
			} else {
				fmt.Printf(" ")
			}
		}
		fmt.Printf("\n")
	}
}