Solve day 04

src/bin/04.rs

@@ -1,7 +1,7 @@
 advent_of_code::solution!(4);
 
 // Count the number of winning card in hand
-fn count_winning(winning: Vec<&str>, hand: Vec<&str>) -> u32 {
+fn count_matches(winning: Vec<&str>, hand: Vec<&str>) -> u32 {
     let mut counter = 0;
     winning.iter().for_each(|i| {
         hand.iter().for_each(|j| {
@@ -17,16 +17,20 @@ pub fn part_one(input: &str) -> Option<u32> {
     input
         .lines()
         .map(|line| {
-            let input_line: Vec<_> = line.split(": ").collect();
-            let numbers: Vec<_> = input_line[1].split(" | ").collect();
+            // Find where card numbers begin ':' and
+            // where to separate left and right cards '|'
+            let (card_index, number_index) = find_indexes(line);
 
-            let winning: Vec<&str> = numbers[0].split_whitespace().collect();
-            let hand: Vec<&str> = numbers[1].split_whitespace().collect();
+            // Extract card information from line
+            let cards_left: Vec<_> = line[card_index + 2..number_index - 1]
+                .split_whitespace()
+                .collect();
+            let cards_right: Vec<_> = line[number_index + 2..].split_whitespace().collect();
 
-            let count = count_winning(winning, hand);
-            let points = match count {
+            let win_count = count_matches(cards_left, cards_right);
+            let points = match win_count {
                 0 => 0,
-                _ => 1 << count - 1, // Double by every winning card
+                _ => 1 << win_count - 1, // Double by every winning card
             };
 
             points
@@ -36,8 +40,48 @@ pub fn part_one(input: &str) -> Option<u32> {
         .ok()
 }
 
-pub fn part_two(_input: &str) -> Option<u32> {
-    None
+fn find_indexes(line: &str) -> (usize, usize) {
+    let mut card_index = 0;
+    let mut number_index = 0;
+
+    for (i, c) in line.chars().enumerate() {
+        if c == ':' {
+            card_index = i;
+        } else if c == '|' {
+            number_index = i;
+            break;
+        }
+    }
+    (card_index, number_index)
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let lines: Vec<_> = input.lines().collect();
+    let max_cards = lines.len();
+    let mut scratchcards: Vec<u32> = vec![1; max_cards]; // Count original cards
+
+    lines.iter().enumerate().for_each(|(card_id, line)| {
+        // Find where card numbers begin ':' and
+        // where to separate left and right cards '|'
+        let (card_index, number_index) = find_indexes(line);
+
+        // Extract card information from line
+        let cards_left: Vec<_> = line[card_index + 2..number_index - 1]
+            .split_whitespace()
+            .collect();
+        let cards_right: Vec<_> = line[number_index + 2..].split_whitespace().collect();
+
+        // Count the number of next cards to copy
+        let next_cards = count_matches(cards_left, cards_right);
+
+        // Add copies to the next cards, counting previously copied cards
+        for i in 1..next_cards + 1 {
+            scratchcards[card_id + i as usize] += 1 * scratchcards[card_id]; // next_copies += 1 * current_copies;
+        }
+    });
+
+    // Return the final number of cards
+    Some(scratchcards.iter().sum::<u32>())
 }
 
 #[cfg(test)]
@@ -53,6 +97,6 @@ mod tests {
     #[test]
     fn test_part_two() {
         let result = part_two(&advent_of_code::template::read_file("examples", DAY));
-        assert_eq!(result, None);
+        assert_eq!(result, Some(30));
     }
 }