Day 4 - Part 2

Signed-off-by: Anthony Oteri <anthony.oteri@gmail.com>

day-04/src/main.rs

@@ -1,3 +1,5 @@
+use std::collections::BTreeMap;
+
 #[derive(Debug, Clone, Default, Eq, PartialEq)]
 struct Card {
     id: usize,
@@ -13,12 +15,15 @@ impl Card {
                 count += 1;
             }
         }
+        count
+    }
 
-        let base: usize = 2;
-        if count == 0 {
+    fn value(&self) -> usize {
+        let num_wins = self.winner();
+        if num_wins == 0 {
             return 0;
         }
-        base.pow(count - 1)
+        2_usize.pow(num_wins as u32 - 1)
     }
 }
 
@@ -53,15 +58,41 @@ fn parse_input(input: &str) -> Vec<Card> {
     cards
 }
 
+fn make_pass(input: &Vec<Card>, cards: &BTreeMap<usize, Card>) -> Vec<Card> {
+    let mut output = Vec::new();
+    for card in input {
+        let win_count = card.winner();
+        for j in card.id + 1..card.id + win_count + 1 {
+            output.push(cards.get(&j).unwrap().clone());
+        }
+    }
+    output
+}
+
 fn part_1(input: &str) -> usize {
     let cards = parse_input(input);
 
-    let total: usize = cards.iter().map(|c| c.winner()).sum();
+    let total: usize = cards.iter().map(|c| c.value()).sum();
     total
 }
 
-fn part_2(_input: &str) -> u32 {
-    0
+fn part_2(input: &str) -> usize {
+    let mut cards = parse_input(input);
+    let cards_by_id = BTreeMap::from_iter(cards.iter().map(|c| (c.id, c.clone())));
+
+    let mut result = Vec::new();
+    result.append(&mut cards.clone());
+
+    loop {
+        let pass = make_pass(&cards, &cards_by_id);
+        if pass.is_empty() {
+            break;
+        }
+        result.append(&mut pass.clone());
+        cards = pass;
+    }
+
+    result.len()
 }
 
 fn main() {
@@ -82,12 +113,31 @@ mod test {
             game_numbers: vec![83, 86, 6, 31, 17, 9, 48, 53],
         };
 
-        assert_eq!(card.winner(), 8)
+        assert_eq!(card.winner(), 4);
     }
+
+    #[test]
+    fn test_value() {
+        let card = Card {
+            id: 1,
+            winning_numbers: vec![41, 48, 83, 86, 17],
+            game_numbers: vec![83, 86, 6, 31, 17, 9, 48, 53],
+        };
+
+        assert_eq!(card.value(), 8);
+    }
+
     #[test]
     fn test_part_1() {
         let input = include_str!("../test-input.txt");
 
         assert_eq!(part_1(input), 13);
     }
+
+    #[test]
+    fn test_part_2() {
+        let input = include_str!("../test-input.txt");
+
+        assert_eq!(part_2(input), 30);
+    }
 }