Day19

2024/gareth/day19/day19.go

@@ -0,0 +1,90 @@
+package day19
+
+import (
+	"strings"
+)
+
+func Part1(input string) int {
+	towelPatterns, designs := parseInput(input)
+	result := countPossibleDesigns(towelPatterns, designs)
+	return result
+}
+
+func Part2(input string) int {
+	towelPatterns, designs := parseInput(input)
+	result := totalArrangements(towelPatterns, designs)
+	return result
+}
+
+func parseInput(input string) ([]string, []string) {
+	parts := strings.SplitN(input, "\n\n", 2)
+	towels := strings.Split(strings.ReplaceAll(parts[0], " ", ""), ",")
+	patterns := strings.Split(strings.TrimSpace(parts[1]), "\n")
+	return towels, patterns
+}
+
+func countPossibleDesigns(towelPatterns []string, designs []string) int {
+	memo := make(map[string]bool)
+	count := 0
+
+	for _, design := range designs {
+		if canConstruct(design, towelPatterns, memo) {
+			count++
+		}
+	}
+
+	return count
+}
+
+func canConstruct(design string, patterns []string, memo map[string]bool) bool {
+	if design == "" {
+		return true
+	}
+	if val, found := memo[design]; found {
+		return val
+	}
+
+	for _, pattern := range patterns {
+		if strings.HasPrefix(design, pattern) {
+			remaining := design[len(pattern):]
+			if canConstruct(remaining, patterns, memo) {
+				memo[design] = true
+				return true
+			}
+		}
+	}
+
+	memo[design] = false
+	return false
+}
+
+func totalArrangements(towelPatterns []string, designs []string) int {
+	memo := make(map[string]int)
+	total := 0
+
+	for _, design := range designs {
+		total += countWays(design, towelPatterns, memo)
+	}
+
+	return total
+}
+
+func countWays(design string, patterns []string, memo map[string]int) int {
+	if design == "" {
+		return 1
+	}
+	if val, found := memo[design]; found {
+		return val
+	}
+
+	totalWays := 0
+	for _, pattern := range patterns {
+		if strings.HasPrefix(design, pattern) {
+			remaining := design[len(pattern):]
+			totalWays += countWays(remaining, patterns, memo)
+		}
+	}
+
+	memo[design] = totalWays
+	return totalWays
+}