Solution for 2024, day 19

Author: lucianoq

2024/19/Makefile

@@ -0,0 +1,20 @@
+input:
+	http "https://adventofcode.com/2024/day/19/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
+

2024/19/common.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"bufio"
+	"os"
+	"strings"
+)
+
+func parseInput() ([]string, []string) {
+	scanner := bufio.NewScanner(os.Stdin)
+	scanner.Scan()
+	patterns := strings.Split(scanner.Text(), ", ")
+	scanner.Scan()
+	designs := make([]string, 0)
+	for scanner.Scan() {
+		designs = append(designs, scanner.Text())
+	}
+	return patterns, designs
+}

2024/19/main1.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func main() {
+	patterns, designs := parseInput()
+
+	cache := map[string]bool{}
+
+	sum := 0
+	for _, d := range designs {
+		if possible(d, patterns, cache) {
+			sum++
+		}
+	}
+	fmt.Println(sum)
+}
+
+func possible(d string, patterns []string, cache map[string]bool) bool {
+	if len(d) == 0 {
+		return true
+	}
+
+	if t, ok := cache[d]; ok {
+		return t
+	}
+
+	for _, p := range patterns {
+		if strings.HasPrefix(d, p) {
+			found := possible(d[len(p):], patterns, cache)
+			if found {
+				cache[d] = true
+				return true
+			}
+		}
+	}
+
+	cache[d] = false
+	return false
+}

2024/19/main1_bad.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+)
+
+func main() {
+	patterns, designs := parseInput()
+
+	rgxp := regexp.MustCompile(fmt.Sprintf("^(%s)+$", strings.Join(patterns, "|")))
+
+	sum := 0
+	for _, d := range designs {
+		if rgxp.MatchString(d) {
+			sum++
+		}
+	}
+	fmt.Println(sum)
+}

2024/19/main2.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func main() {
+	patterns, designs := parseInput()
+
+	cache := map[string]int{}
+
+	sum := 0
+	for _, d := range designs {
+		sum += ways(d, patterns, cache)
+	}
+	fmt.Println(sum)
+}
+
+func ways(d string, patterns []string, cache map[string]int) int {
+	if len(d) == 0 {
+		return 1
+	}
+
+	if w, ok := cache[d]; ok {
+		return w
+	}
+
+	w := 0
+	for _, p := range patterns {
+		if strings.HasPrefix(d, p) {
+			w += ways(d[len(p):], patterns, cache)
+		}
+	}
+
+	cache[d] = w
+	return w
+}