Day 19

1 files changed, 105 insertions, 0 deletions

diff --git a/day19/main.go b/day19/main.go
new file mode 100644
index 0000000..96dac55
--- /dev/null
+++ b/day19/main.go
@@ -0,0 +1,105 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+)
+
+func main() {
+	patterns, targets := readData("example.txt")
+	fmt.Println(part1(patterns, targets), 6)
+	fmt.Println(part2(patterns, targets), 16)
+
+	patterns, targets = readData("data.txt")
+	fmt.Println(part1(patterns, targets), 280)
+	fmt.Println(part2(patterns, targets))
+}
+
+func part1(patterns []string, targets []string) (okCount int) {
+	notFound := make(map[string]bool)
+	for _, target := range targets {
+		if doable(patterns, target, notFound) {
+			okCount++
+		}
+	}
+	return
+}
+
+func part2(patterns []string, targets []string) (okCount int) {
+	combis := make(map[string]int)
+	for _, target := range targets {
+		okCount += combinations(patterns, target, combis)
+	}
+	return
+}
+
+func combinations(patterns []string, target string, combis map[string]int) (combiCount int) {
+	if combiCountCache, ok := combis[target]; ok {
+		return combiCountCache
+	}
+
+	for _, p := range patterns {
+		if len(p) > len(target) {
+			continue
+		}
+		if target[:len(p)] != p {
+			continue
+		}
+
+		if len(p) == len(target) {
+			if p == target {
+				combiCount++
+			}
+		} else {
+			combiCount += combinations(patterns, target[len(p):], combis)
+		}
+	}
+
+	combis[target] = combiCount
+	return
+}
+
+func doable(patterns []string, target string, notFound map[string]bool) bool {
+	if len(target) == 0 {
+		return true
+	}
+
+	if _, n := notFound[target]; n {
+		return false
+	}
+
+	for _, p := range patterns {
+		if len(p) > len(target) {
+			continue
+		}
+		if target[:len(p)] != p {
+			continue
+		}
+		if doable(patterns, target[len(p):], notFound) {
+			return true
+		}
+	}
+
+	notFound[target] = true
+	return false
+}
+
+func readData(fileName string) (patterns []string, targets []string) {
+	fp, _ := os.Open(fileName)
+	scanner := bufio.NewScanner(fp)
+
+	scanner.Scan()
+	patterns = strings.Split(scanner.Text(), ",")
+	for i, p := range patterns {
+		patterns[i] = strings.TrimSpace(p)
+	}
+
+	scanner.Scan()
+	for scanner.Scan() {
+		targets = append(targets, strings.TrimSpace(scanner.Text()))
+	}
+
+	return
+}