Solve day 19 part 2

src/bin/day19/main.rs

@@ -1,3 +1,5 @@
+use ahash::{HashMap, HashMapExt};
+
 const ACTUAL_INPUT: &str = include_str!("../../../actual_inputs/2024/19/input.txt");
 
 fn p1(input: &str) -> String {
@@ -35,8 +37,54 @@ fn p1(input: &str) -> String {
 }
 
 fn p2(input: &str) -> String {
-    let _input = input.trim();
-    "".to_string()
+    let (towels, patterns) = input
+        .trim()
+        .split_once("\n\n")
+        .expect("input has two sections");
+
+    let towels = towels.split(",").map(|s| s.trim()).collect::<Vec<_>>();
+    let patterns = patterns.lines().map(|s| s.trim()).collect::<Vec<_>>();
+    let mut dp: HashMap<&str, usize> = HashMap::new();
+
+    patterns
+        .into_iter()
+        .map(|pattern| {
+            fn check<'a>(
+                dp: &mut HashMap<&'a str, usize>,
+                pattern: &'a str,
+                towels: &[&str],
+                current_idx: usize,
+            ) -> usize {
+                if current_idx == pattern.len() {
+                    1
+                } else {
+                    let substring = &pattern[current_idx..];
+                    if let Some(count) = dp.get(&substring) {
+                        *count
+                    } else {
+                        let count = towels
+                            .iter()
+                            .map(|towel| {
+                                if pattern.len() - current_idx >= towel.len()
+                                    && pattern[current_idx..(current_idx + towel.len())] == **towel
+                                {
+                                    check(dp, pattern, towels, current_idx + towel.len())
+                                } else {
+                                    0
+                                }
+                            })
+                            .sum::<usize>();
+
+                        dp.insert(substring, count);
+                        count
+                    }
+                }
+            }
+
+            check(&mut dp, pattern, &towels, 0)
+        })
+        .sum::<usize>()
+        .to_string()
 }
 
 fn main() {
@@ -73,12 +121,11 @@ bbrgwb
 
     #[test]
     fn test_p2_sample() {
-        assert_eq!(p2(SAMPLE_INPUT), "");
+        assert_eq!(p2(SAMPLE_INPUT), "16");
     }
 
     #[test]
-    #[ignore = "not yet implemented"]
     fn test_p2_actual() {
-        assert_eq!(p2(ACTUAL_INPUT), "");
+        assert_eq!(p2(ACTUAL_INPUT), "717561822679428");
     }
 }