Solve part two of day04.

day04/Cargo.toml

@@ -11,4 +11,8 @@ publish.workspace = true
 [[bin]]
 name = "day04_part1"
 
+[[bin]]
+name = "day04_part2"
+
 [dependencies]
+regex = "1.10.2"

day04/src/bin/day04_part2.rs

@@ -0,0 +1,69 @@
+use std::collections::HashSet;
+use std::str::FromStr;
+
+struct Card {
+    winning_numbers: HashSet<u64>,
+    present_numbers: HashSet<u64>
+}
+
+fn parse_input(input: &str) -> Vec<Card> {
+
+    let mut cards: Vec<Card> = Vec::new();
+    for line in input.lines() {
+        let splits: Vec<&str> = line.split_terminator(&[':', '|'][..]).collect();
+        if splits.len() != 3 {
+            eprintln!("Line: {} is not formatted correctly!", line);
+            continue
+        }
+
+        let winning_numbers: HashSet<u64> = (splits[1]).split_whitespace().map(|x| u64::from_str(x).unwrap()).collect();
+        let present_numbers: HashSet<u64> = (splits[2]).split_whitespace().map(|x| u64::from_str(x).unwrap()).collect();
+        cards.push(Card { winning_numbers, present_numbers});
+    }
+    cards
+}
+
+
+fn calculate_card_value(card: &Card) -> usize {
+    card.present_numbers.intersection(&card.winning_numbers).count()
+}
+
+fn calculate_result(cards: Vec<Card>) -> u64 {
+    let no_of_cards: usize = cards.len();
+    let card_wins: Vec<u64> = cards.iter().map(|card| calculate_card_value(card) as u64).collect();
+    let mut card_count: Vec<u64> = vec![1; no_of_cards];
+
+    let mut result: u64 = 0;
+
+    for idx in 0..no_of_cards {
+        let wins = card_wins[idx];
+        let count = card_count[idx];
+
+        for idy in & mut card_count [idx+1..idx+ (wins as usize) + 1] {
+            *idy += count;
+        }
+        result += count;
+    }
+    result
+}
+
+fn main() {
+
+    let input = include_str!("../../resources/input_01.txt");
+    let cards = parse_input(input);
+    let res = calculate_result(cards);
+    println!("{}", res);
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_input01() {
+        let input = include_str!("../../resources/test_input_01.txt");
+        let cards = parse_input(input);
+        let res = calculate_result(cards);
+        assert_eq!(res, 30);
+    }
+}