day 3 and 4 solutions

src/day04.rs

@@ -0,0 +1,96 @@
+use crate::utils::read_file;
+use anyhow::Result;
+
+#[derive(Debug)]
+struct Bingo {
+    draws: Vec<usize>,
+    boards: Vec<Vec<usize>>,
+}
+
+fn parse_bingo(s: &str) -> Bingo {
+    Bingo {
+        // take the first line and split on comma
+        draws: s
+            .lines()
+            .next()
+            .unwrap()
+            .split(',')
+            .map(|s| s.parse::<usize>().unwrap())
+            .collect(),
+        // split on whitespace, collect all the remaining numbers and then chunk them out in 25s
+        boards: s
+            .lines()
+            .skip(2)
+            .map(|line| line.split_whitespace().map(|s| s.parse::<usize>().unwrap()))
+            .flatten()
+            .collect::<Vec<usize>>()
+            .chunks(25)
+            .map(|c| c.into())
+            .collect(),
+    }
+}
+
+fn test_for_win(marked: usize) -> bool {
+    let col_mask: usize = 0b1000010000100001000010000;
+    let row_mask: usize = 0b1111100000000000000000000;
+    (0..5).any(|i| {
+        marked & (col_mask >> i) == (col_mask >> i)
+            || marked & (row_mask >> (i * 5)) == (row_mask >> (i * 5))
+    })
+}
+
+fn compute_score(board: &[usize], marked: usize, last_draw: usize) -> usize {
+    (0..25)
+        .map(|i| if marked & 1 << i == 0 { board[i] } else { 0 })
+        .sum::<usize>()
+        * last_draw
+}
+
+fn find_winning_score(s: &str, first: bool) -> usize {
+    let bingo = parse_bingo(s);
+    let mut markers = vec![0; bingo.boards.len()];
+    let mut boards_won = vec![false; bingo.boards.len()];
+    // for every drawn number, mark each board and check whether it wins
+    for draw in bingo.draws {
+        for i in 0..bingo.boards.len() {
+            for j in 0..bingo.boards[i].len() {
+                if bingo.boards[i][j] == draw {
+                    markers[i] |= 1 << j;
+                }
+                if test_for_win(markers[i]) {
+                    boards_won[i] = true;
+                    if first || (!first && boards_won.iter().all(|w| *w)) {
+                        return compute_score(&bingo.boards[i], markers[i], draw);
+                    }
+                }
+            }
+        }
+    }
+    unreachable!()
+}
+
+pub(crate) fn run() -> Result<(usize, usize)> {
+    let input = read_file("data/day04.txt")?;
+    Ok((
+        find_winning_score(&input, true),
+        find_winning_score(&input, false),
+    ))
+}
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_example() {
+        let input = read_file("data/day04-test.txt").unwrap();
+        assert_eq!(find_winning_score(&input, true), 4512);
+        assert_eq!(find_winning_score(&input, false), 1924);
+    }
+
+    #[test]
+    fn test_my_data() {
+        let input = read_file("data/day04.txt").unwrap();
+        assert_eq!(find_winning_score(&input, true), 71708);
+        assert_eq!(find_winning_score(&input, false), 34726);
+    }
+}