day four part two

four/output-two

@@ -0,0 +1 @@
+8736438

four/src/two.rs

@@ -3,4 +3,47 @@ use std::io::{self, Read};
 fn main() {
     let mut buf = String::new();
     io::stdin().read_to_string(&mut buf).unwrap();
+
+    let wins_by_card: Vec<_> = buf
+        .lines()
+        .map(|l| &l[5..])
+        .map(|l| [&l[5..34], &l[37..]])
+        .map(|[winners, numbers]| {
+            (
+                winners
+                    .split(' ')
+                    .filter(|str| str != &"")
+                    .map(str::trim)
+                    .flat_map(|num_str| num_str.parse::<usize>())
+                    .collect::<Vec<_>>(),
+                numbers
+                    .split(' ')
+                    .filter(|str| str != &"")
+                    .map(str::trim)
+                    .flat_map(|num_str| num_str.parse::<usize>())
+                    .collect::<Vec<_>>(),
+            )
+        })
+        .map(|(winners, numbers)| {
+            numbers
+                .iter()
+                .filter(|number| winners.contains(number))
+                .count()
+        })
+        .collect();
+
+    let mut copies_by_card = vec![1; wins_by_card.len()];
+
+    wins_by_card.iter().enumerate().for_each(|(idx, wins)| {
+        let copies_of_winner = copies_by_card[idx];
+        copies_by_card
+            .iter_mut()
+            .skip(idx + 1)
+            .take(*wins)
+            .for_each(|copies| *copies += copies_of_winner)
+    });
+
+    let total: usize = copies_by_card.iter().sum();
+
+    println!("{total}");
 }