Day21

2024/gareth/day21/day21.go

@@ -0,0 +1,125 @@
+package day21
+
+import (
+	"strconv"
+	"strings"
+)
+
+type coordinate struct {
+	row, col int
+}
+
+var numberPad = map[string]coordinate{
+	"7": {0, 0}, "8": {0, 1}, "9": {0, 2},
+	"4": {1, 0}, "5": {1, 1}, "6": {1, 2},
+	"1": {2, 0}, "2": {2, 1}, "3": {2, 2},
+	"0": {3, 1}, "A": {3, 2},
+}
+
+var robotPad = map[string]coordinate{
+	"^": {0, 1}, "A": {0, 2},
+	"<": {1, 0}, "v": {1, 1}, ">": {1, 2},
+}
+
+type cacheKey struct {
+	sequence   string
+	iterations int
+}
+
+var memo = make(map[cacheKey]int)
+
+func Part1(input string) int {
+	codes := parseInput(input)
+
+	numpadGraph := createGraph(numberPad, coordinate{3, 0})
+	dirpadGraph := createGraph(robotPad, coordinate{0, 0})
+
+	total := 0
+	for _, code := range codes {
+		codeInt, _ := strconv.Atoi(code[:len(code)-1])
+		total += codeInt * getLength(code, 3, true, numpadGraph, dirpadGraph)
+	}
+	return total
+}
+
+func Part2(input string) int {
+	codes := parseInput(input)
+
+	numpadGraph := createGraph(numberPad, coordinate{3, 0})
+	dirpadGraph := createGraph(robotPad, coordinate{0, 0})
+
+	total := 0
+	for _, code := range codes {
+		codeInt, _ := strconv.Atoi(code[:len(code)-1])
+		total += codeInt * getLength(code, 26, true, numpadGraph, dirpadGraph)
+	}
+	return total
+}
+
+func parseInput(input string) []string {
+	parts := strings.Split(input, "\n")
+	codes := []string{}
+	codes = append(codes, parts...)
+	return codes
+}
+
+func createGraph(keypad map[string]coordinate, invalidCoords coordinate) map[string]string {
+	graph := make(map[string]string)
+
+	for a, coordA := range keypad {
+		for b, coordB := range keypad {
+			x1, y1 := coordA.row, coordA.col
+			x2, y2 := coordB.row, coordB.col
+
+			path := strings.Repeat("<", max(0, y1-y2)) +
+				strings.Repeat("v", max(0, x2-x1)) +
+				strings.Repeat("^", max(0, x1-x2)) +
+				strings.Repeat(">", max(0, y2-y1))
+
+			if invalidCoords == (coordinate{x1, y2}) || invalidCoords == (coordinate{x2, y1}) {
+				path = reverseString(path)
+			}
+			graph[a+"->"+b] = path + "A"
+		}
+	}
+
+	return graph
+}
+
+func reverseString(s string) string {
+	runes := []rune(s)
+	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
+		runes[i], runes[j] = runes[j], runes[i]
+	}
+	return string(runes)
+}
+
+func getLength(sequence string, iterations int, firstIter bool, numpadGraph map[string]string, dirpadGraph map[string]string) int {
+
+	if iterations == 0 {
+		return len(sequence)
+	}
+
+	key := cacheKey{sequence: sequence, iterations: iterations}
+	if cachedResult, exists := memo[key]; exists {
+		return cachedResult
+	}
+
+	graph := numpadGraph
+	if !firstIter {
+		graph = dirpadGraph
+	}
+
+	totalLength := 0
+	prev := "A"
+	for _, char := range sequence {
+		graphKey := prev + "->" + string(char)
+		if subSequence, exists := graph[graphKey]; exists {
+			totalLength += getLength(subSequence, iterations-1, false, numpadGraph, dirpadGraph)
+		}
+		prev = string(char)
+	}
+
+	memo[key] = totalLength
+	return totalLength
+}

2024/gareth/day21/day21_test.go

@@ -0,0 +1,25 @@
+package day21
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPart1(t *testing.T) {
+	r := Part1(`029A
+980A
+179A
+456A
+379A`)
+	assert.Equal(t, 126384, r)
+}
+
+func TestPart2(t *testing.T) {
+	r := Part2(`029A
+980A
+179A
+456A
+379A`)
+	assert.Equal(t, 126384, r)
+}

2024/gareth/day21/input.txt

@@ -0,0 +1,5 @@
+985A
+540A
+463A
+671A
+382A

2024/gareth/main.go

@@ -1,7 +1,7 @@
 package main
 
 import (
-	"aoc2024/day20"
+	"aoc2024/day21"
 	"fmt"
 	"os"
 	"time"
@@ -9,9 +9,9 @@ import (
 
 func main() {
 	start := time.Now()
-	data, _ := os.ReadFile("day20/input.txt")
-	fmt.Printf("part 1: %d\n", day20.Part1(string(data)))
-	fmt.Printf("part 2: %d\n", day20.Part2(string(data)))
+	data, _ := os.ReadFile("day21/input.txt")
+	fmt.Printf("part 1: %d\n", day21.Part1(string(data)))
+	fmt.Printf("part 2: %d\n", day21.Part2(string(data)))
 	elapsed := time.Since(start)
 	fmt.Printf("Execution time: %s\n", elapsed)
 }