AdventOfCode2020/11/main.go

package main

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

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)
}

type cell struct {
	taken int  // 1: someone there; 0: empty
	seat  bool // t: seat available; f: open floor
}

type waitingRoom struct {
	seats  [][]cell
	maxCol int
	maxRow int
}

func (w *waitingRoom) parseRow(s string) {
	row := []cell{}

	for _, r := range s {
		switch {
		case r == 'L':
			row = append(row, cell{taken: 0, seat: true})
		case r == '.':
			row = append(row, cell{taken: 0, seat: false})
		}
	}
	w.seats = append(w.seats, row)
}

func (w *waitingRoom) countNeighborsPartOne(row, col int) int {
	c := 0
	if row-1 > -1 {
		c = c + w.seats[row-1][col].taken // north
		if col-1 > -1 {
			c = c + w.seats[row-1][col-1].taken // northwest
		}
		if col+1 < w.maxCol {
			c = c + w.seats[row-1][col+1].taken // northheast
		}
	}
	if row+1 < w.maxRow {
		c = c + w.seats[row+1][col].taken // south
		if col+1 < w.maxCol {
			c = c + w.seats[row+1][col+1].taken // southeast
		}
		if col-1 > -1 {
			c = c + w.seats[row+1][col-1].taken // southwest
		}
	}
	if col-1 > -1 {
		c = c + w.seats[row][col-1].taken // west
	}
	if col+1 < w.maxCol {
		c = c + w.seats[row][col+1].taken // east
	}
	return c
}

func (w *waitingRoom) makeNextStepPartOne() *waitingRoom {
	newRoom := &waitingRoom{
		seats:  make([][]cell, w.maxRow),
		maxCol: w.maxCol,
		maxRow: w.maxRow,
	}

	for r := range w.seats {
		newRoom.seats[r] = make([]cell, newRoom.maxCol)
		for c := range w.seats[r] {
			if w.seats[r][c].seat && w.seats[r][c].taken == 0 && w.countNeighborsPartOne(r, c) == 0 {
				newRoom.seats[r][c].seat = w.seats[r][c].seat
				newRoom.seats[r][c].taken = 1
			} else if w.seats[r][c].seat && w.seats[r][c].taken == 1 && w.countNeighborsPartOne(r, c) >= 4 {
				newRoom.seats[r][c].seat = w.seats[r][c].seat
				newRoom.seats[r][c].taken = 0
			} else {
				newRoom.seats[r][c].seat = w.seats[r][c].seat
				newRoom.seats[r][c].taken = w.seats[r][c].taken
			}
		}
	}

	return newRoom
}

func (w *waitingRoom) countNeighborsPartTwo(row, col int) int {
	c := 0
	trow := row
	tcol := col

	// south
	for trow < w.maxRow-1 {
		trow = trow + 1
		if w.seats[trow][col].seat {
			c = c + w.seats[trow][col].taken
			break
		}
	}
	trow = row

	// north
	for trow > 0 {
		trow = trow - 1
		if w.seats[trow][col].seat {
			c = c + w.seats[trow][col].taken
			break
		}
	}
	trow = row

	// west
	for tcol > 0 {
		tcol = tcol - 1
		if w.seats[row][tcol].seat {
			c = c + w.seats[row][tcol].taken
			break
		}
	}
	tcol = col

	// east
	for tcol < w.maxCol-1 {
		tcol = tcol + 1
		if w.seats[row][tcol].seat {
			c = c + w.seats[row][tcol].taken
			break
		}
	}
	tcol = col

	// southeast
	for trow < w.maxRow-1 && tcol < w.maxCol-1 {
		trow = trow + 1
		tcol = tcol + 1
		if w.seats[trow][tcol].seat {
			c = c + w.seats[trow][tcol].taken
			break
		}
	}
	trow = row
	tcol = col

	// southwest
	for trow < w.maxRow-1 && tcol > 0 {
		trow = trow + 1
		tcol = tcol - 1
		if w.seats[trow][tcol].seat {
			c = c + w.seats[trow][tcol].taken
			break
		}
	}
	trow = row
	tcol = col

	// northeast
	for trow > 0 && tcol < w.maxCol-1 {
		trow = trow - 1
		tcol = tcol + 1
		if w.seats[trow][tcol].seat {
			c = c + w.seats[trow][tcol].taken
			break
		}
	}
	trow = row
	tcol = col

	// northwest
	for trow > 0 && tcol > 0 {
		trow = trow - 1
		tcol = tcol - 1
		if w.seats[trow][tcol].seat {
			c = c + w.seats[trow][tcol].taken
			break
		}
	}

	return c
}

func (w *waitingRoom) makeNextStepPartTwo() *waitingRoom {
	newRoom := &waitingRoom{
		seats:  make([][]cell, w.maxRow),
		maxCol: w.maxCol,
		maxRow: w.maxRow,
	}

	for r := range w.seats {
		newRoom.seats[r] = make([]cell, newRoom.maxCol)
		for c := range w.seats[r] {
			if w.seats[r][c].seat && w.seats[r][c].taken == 0 && w.countNeighborsPartTwo(r, c) == 0 {
				newRoom.seats[r][c].seat = w.seats[r][c].seat
				newRoom.seats[r][c].taken = 1
			} else if w.seats[r][c].seat && w.seats[r][c].taken == 1 && w.countNeighborsPartTwo(r, c) >= 5 {
				newRoom.seats[r][c].seat = w.seats[r][c].seat
				newRoom.seats[r][c].taken = 0
			} else {
				newRoom.seats[r][c].seat = w.seats[r][c].seat
				newRoom.seats[r][c].taken = w.seats[r][c].taken
			}
		}
	}

	return newRoom
}

func (w *waitingRoom) countFilledSeats() int {
	count := 0
	for r := range w.seats {
		for c := range w.seats[r] {
			count = count + w.seats[r][c].taken
		}
	}
	return count
}

func (w *waitingRoom) print() {
	for r := range w.seats {
		s := ""
		for c := range w.seats[r] {
			if !w.seats[r][c].seat {
				s = s + "."
			} else if w.seats[r][c].taken == 0 {
				s = s + "L"
			} else if w.seats[r][c].taken == 1 {
				s = s + "#"
			}
		}
		fmt.Println(s)
	}
}

func checkStasis(old, new *waitingRoom) bool {
	for r := range old.seats {
		for c := range old.seats[r] {
			if old.seats[r][c].seat && old.seats[r][c].taken != new.seats[r][c].taken {
				return false
			}
		}
	}
	return true
}

func partOne() {
	f, _ := os.Open("input")
	reader := bufio.NewReader(f)
	scanner := bufio.NewScanner(reader)

	oldRoom := &waitingRoom{}

	for scanner.Scan() {
		line := scanner.Text()
		oldRoom.parseRow(line)
	}

	oldRoom.maxCol = len(oldRoom.seats[0])
	oldRoom.maxRow = len(oldRoom.seats)

	for {
		newRoom := oldRoom.makeNextStepPartOne()
		if checkStasis(newRoom, oldRoom) {
			fmt.Println(newRoom.countFilledSeats())
			return
		}
		oldRoom = newRoom
	}
}

func partTwo() {
	f, _ := os.Open("input")
	reader := bufio.NewReader(f)
	scanner := bufio.NewScanner(reader)
	oldRoom := &waitingRoom{}

	for scanner.Scan() {
		line := scanner.Text()
		oldRoom.parseRow(line)
	}

	oldRoom.maxCol = len(oldRoom.seats[0])
	oldRoom.maxRow = len(oldRoom.seats)

	for {
		newRoom := oldRoom.makeNextStepPartTwo()
		if checkStasis(newRoom, oldRoom) {
			fmt.Println(newRoom.countFilledSeats())
			return
		}
		oldRoom = newRoom
	}
}