day 11 ended up being a _lot_ of code

10/main.go

@@ -0,0 +1,117 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"sort"
+	"strconv"
+)
+
+func main() {
+	partOne()
+	partTwo()
+}
+
+// Find a chain that uses all of your adapters to connect the charging outlet to your device's built-in adapter
+// and count the joltage differences between the charging outlet, the adapters, and your device.
+// What is the number of 1-jolt differences multiplied by the number of 3-jolt differences?
+
+func partOne() {
+	f, _ := os.Open("input")
+	reader := bufio.NewReader(f)
+	scanner := bufio.NewScanner(reader)
+
+	// wall
+	adapters := []int{0}
+
+	// load
+	for scanner.Scan() {
+		line := scanner.Text()
+		i, _ := strconv.Atoi(line)
+		adapters = append(adapters, i)
+	}
+
+	// sort
+	sort.Slice(adapters, func(i, j int) bool {
+		return adapters[i] < adapters[j]
+	})
+
+	// device
+	adapters = append(adapters, adapters[len(adapters)-1]+3)
+
+	one := 0
+	three := 0
+
+	// count gaps
+	for i, j := range adapters {
+		if i < len(adapters)-1 {
+			if adapters[i+1]-j == 3 {
+				three = three + 1
+			} else if adapters[i+1]-j == 1 {
+				one = one + 1
+			}
+		}
+	}
+
+	fmt.Println(three * one)
+}
+
+// You glance back down at your bag and try to remember why you brought so many adapters; there must be more than a trillion valid ways to arrange them!
+// Surely, there must be an efficient way to count the arrangements.
+// What is the total number of distinct ways you can arrange the adapters to connect the charging outlet to your device?
+
+func partTwo() {
+	f, _ := os.Open("input")
+	reader := bufio.NewReader(f)
+	scanner := bufio.NewScanner(reader)
+
+	// wall
+	adapters := []int{0}
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		i, _ := strconv.Atoi(line)
+		adapters = append(adapters, i)
+	}
+
+	// sort
+	sort.Slice(adapters, func(i, j int) bool {
+		return adapters[i] < adapters[j]
+	})
+
+	// device
+	adapters = append(adapters, adapters[len(adapters)-1]+3)
+
+	combinations := 1
+	ones := 0
+	three := 0
+
+	// count gaps
+	for i, j := range adapters {
+		if i < len(adapters)-1 {
+			if adapters[i+1]-j == 1 {
+				// small steps...
+				ones = ones + 1
+			} else if adapters[i+1]-j == 3 {
+				combinations = combinations + 1
+				if ones == 2 {
+					combinations = combinations * 1
+				}
+				if ones == 3 {
+					combinations = combinations * 2
+				}
+				if ones == 4 {
+					combinations = combinations * 4
+				}
+				if ones == 5 {
+					combinations = combinations * 7
+				}
+				ones = 0
+				three = three + 1
+			}
+		}
+	}
+
+	fmt.Println(adapters, combinations)
+}

11/main.go

@@ -0,0 +1,298 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+func main() {
+	partOne()
+	partTwo()
+}
+
+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
+	}
+}