day-14

day-14/go.mod

@@ -0,0 +1,3 @@
+module github.com/onyx-and-iris/aoc2023/day-14
+
+go 1.21.5

day-14/image.go

@@ -0,0 +1,35 @@
+package main
+
+import "fmt"
+
+type img struct {
+	raw []string
+}
+
+func newImg(sz int) img {
+	return img{raw: make([]string, sz)}
+}
+
+// transposed rotates an image rightwards ninety degrees
+func (i img) transposed() []string {
+	transposed := []string{}
+
+	for x := 0; x < len(i.raw[0]); x++ {
+		buf := ""
+		for j := len(i.raw) - 1; j >= 0; j-- {
+			buf += string(i.raw[j][x])
+		}
+		transposed = append(transposed, buf)
+	}
+
+	return transposed
+}
+
+// String implements the Stringer interface
+func (i img) String() string {
+	out := ""
+	for _, line := range i.raw {
+		out += fmt.Sprintf("%s\n", line)
+	}
+	return out
+}

day-14/makefile

@@ -0,0 +1,10 @@
+TEST="test.txt"
+INPUT="input.txt"
+
+test:
+	cat $(TEST) | go run .
+
+run:
+	cat $(INPUT) | go run .
+
+all: test

day-14/one.go

@@ -0,0 +1,57 @@
+package main
+
+const MAX = 10
+
+func getload(raw []string) int {
+	load := 0
+	for _, line := range raw {
+		for i, r := range line {
+			if r == 'O' {
+				load += (i + 1)
+			}
+		}
+	}
+
+	return load
+}
+
+func spacesToRight(i int, line string) int {
+	num := 0
+outer:
+	for i += 1; i < len(line); i++ {
+		switch line[i] {
+		case '.':
+			num++
+		case '#', 'O':
+			break outer
+		}
+	}
+	return num
+}
+
+func rollRight(line string) string {
+	for i := len(line) - 1; i >= 0; i-- {
+		if line[i] == 'O' {
+			n := spacesToRight(i, line)
+			if n == 0 {
+				continue
+			}
+			line = replaceAtIndex(line, '.', i)
+			line = replaceAtIndex(line, 'O', i+n)
+		}
+	}
+
+	return line
+}
+
+// one returns the load of all boulders after a single image cycle
+func one(lines []string) int {
+	image := newImg(len(lines))
+	copy(image.raw, lines)
+
+	for i, line := range image.transposed() {
+		image.raw[i] = rollRight(line)
+	}
+
+	return getload(image.raw)
+}

day-14/solution.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"fmt"
+
+	log "github.com/sirupsen/logrus"
+)
+
+func init() {
+	log.SetLevel(log.InfoLevel)
+}
+
+func main() {
+	lines := readlines()
+
+	ans := one(lines)
+	fmt.Printf("solution one: %d\n", ans)
+
+	ans = two(lines)
+	fmt.Printf("solution two: %d\n", ans)
+}

day-14/two.go

@@ -0,0 +1,45 @@
+package main
+
+const CYCLES = 1000000000
+
+// cycleOnce transposes and rolls a single image once
+func cycleOnce(image img) {
+	for i := 0; i < 4; i++ {
+		for i, line := range image.transposed() {
+			image.raw[i] = rollRight(line)
+		}
+	}
+}
+
+// cycleMany cycles a single image for a given number of iterations
+// it also caches each image and measures the period of repetition
+func cycleMany(image img, iterations int) {
+	cache := make(map[string]int)
+	i, start := 0, 0
+	for ; i < iterations; i++ {
+		cycleOnce(image)
+
+		if idx, ok := cache[image.String()]; ok { // we found first repeated image
+			start = idx
+			i++
+			break
+		}
+
+		cache[image.String()] = i + 1
+	}
+	period := i - start                        // length of a full period
+	remaining := (iterations - i - 1) % period // number of cycles left in current period
+	for j := 0; j < remaining; j++ {
+		cycleOnce(image) // rotate to the final image in the period
+	}
+}
+
+// two returns the load of all boulders after 1000000000 cycles
+func two(lines []string) int {
+	image := newImg(len(lines))
+	copy(image.raw, lines)
+
+	cycleMany(image, CYCLES)
+
+	return getload(image.transposed())
+}

day-14/util.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"bufio"
+	"log"
+	"os"
+)
+
+// readlines reads lines from stdin.
+// it returns them as an array of strings
+func readlines() []string {
+	lines := []string{}
+
+	scanner := bufio.NewScanner(os.Stdin)
+	for scanner.Scan() {
+		lines = append(lines, scanner.Text())
+	}
+
+	if err := scanner.Err(); err != nil {
+		log.Fatal(err)
+	}
+
+	return lines
+}
+
+// replaceAtIndex replaces a character in a string at index i
+func replaceAtIndex(in string, r rune, i int) string {
+	out := []rune(in)
+	out[i] = r
+	return string(out)
+}