Solution for 2024, day 21

Author: lucianoq

2024/21/Makefile

@@ -0,0 +1,20 @@
+input:
+	http "https://adventofcode.com/2024/day/21/input" "Cookie:session=${AOC_SESSION};" >input
+
+main1:
+	go build -o main1 main1.go common.go
+
+main2:
+	go build -o main2 main2.go common.go
+
+.PHONY: run1 run2 clean
+
+run1: main1 input
+	./main1 <input
+
+run2: main2 input
+	./main2 <input
+
+clean:
+	rm -f main1 main2 input
+

2024/21/common.go

@@ -0,0 +1,152 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type P struct{ x, y int }
+
+var numKeypadMap = map[byte]P{
+	'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},
+	'_': {3, 0}, '0': {3, 1}, 'A': {3, 2},
+}
+
+var dirKeypadMap = map[byte]P{
+	'_': {0, 0}, '^': {0, 1}, 'A': {0, 2},
+	'<': {1, 0}, 'v': {1, 1}, '>': {1, 2},
+}
+
+func main() {
+	codes := parseInput()
+	sum := 0
+	for _, code := range codes {
+		directions := pressNumbers(code)
+		seqLength := press(directions, Depth)
+
+		numericPart, _ := strconv.Atoi(code[:len(code)-1])
+
+		sum += seqLength * numericPart
+	}
+	fmt.Println(sum)
+}
+
+// type for the key in the map for press() memoization
+type key = struct {
+	seq   string
+	depth int
+}
+
+// memoization for press()
+var cachePress = map[key]int{}
+
+// press returns the length of the directional string
+// after applying `depth` times the indirection
+func press(code string, depth int) int {
+	if depth == 0 {
+		return len(code)
+	}
+
+	// check in cache
+	if size, ok := cachePress[key{code, depth}]; ok {
+		return size
+	}
+
+	totalSize := 0
+	for _, chunk := range strings.SplitAfter(code, "A") {
+		totalSize += press(pressDirections(chunk), depth-1)
+	}
+
+	// save into cache
+	cachePress[key{code, depth}] = totalSize
+
+	return totalSize
+}
+
+func pressDirections(dir string) string {
+	hole := dirKeypadMap['_']
+	curr := dirKeypadMap['A']
+
+	seq := ""
+	for _, c := range dir {
+		goal := dirKeypadMap[byte(c)]
+
+		deltaH, deltaV := goal.y-curr.y, goal.x-curr.x
+		hs, vs := getMovements(deltaH, deltaV)
+		seq += prioritize(hs, vs, curr, goal, hole)
+
+		curr.x += deltaV
+		curr.y += deltaH
+
+		seq += "A"
+	}
+	return seq
+}
+
+func pressNumbers(code string) string {
+	hole := numKeypadMap['_']
+	curr := numKeypadMap['A']
+
+	seq := ""
+	for _, c := range code {
+		goal := numKeypadMap[byte(c)]
+
+		deltaH, deltaV := goal.y-curr.y, goal.x-curr.x
+		hs, vs := getMovements(deltaH, deltaV)
+		seq += prioritize(hs, vs, curr, goal, hole)
+
+		curr.x += deltaV
+		curr.y += deltaH
+
+		seq += "A"
+	}
+	return seq
+}
+
+func getMovements(deltaH, deltaV int) (string, string) {
+	var hs, vs string
+	for deltaH > 0 {
+		hs += ">"
+		deltaH--
+	}
+	for deltaH < 0 {
+		hs += "<"
+		deltaH++
+	}
+	for deltaV > 0 {
+		vs += "v"
+		deltaV--
+	}
+	for deltaV < 0 {
+		vs += "^"
+		deltaV++
+	}
+	return hs, vs
+}
+
+func prioritize(hs, vs string, from, to, avoid P) string {
+	switch {
+	case from.x == avoid.x && to.y == avoid.y:
+		return vs + hs
+	case from.y == avoid.y && to.x == avoid.x:
+		return hs + vs
+	case strings.Contains(hs, "<"):
+		return hs + vs
+	default:
+		return vs + hs
+	}
+}
+
+func parseInput() []string {
+	var list []string
+	scanner := bufio.NewScanner(os.Stdin)
+	for scanner.Scan() {
+		list = append(list, scanner.Text())
+	}
+	return list
+}

2024/21/main1.go

@@ -0,0 +1,3 @@
+package main
+
+const Depth = 2

2024/21/main2.go

@@ -0,0 +1,3 @@
+package main
+
+const Depth = 25