Day 4

src/bin/04.rs

@@ -0,0 +1,147 @@
+use std::fmt::Display;
+
+fn main() {
+    println!("First score: {}\n", part1());
+    println!("Second score: {}", part2());
+}
+
+fn part1() -> u32 {
+    let (mut boards, rng) = input();
+
+    for n in rng {
+        for board in &mut boards {
+            board.mark(n);
+            if board.wins() {
+                println!("{}", board);
+                return board.score(n);
+            }
+        }
+    }
+
+    0
+}
+
+fn part2() -> u32 {
+    let (mut boards, mut rng) = input();
+
+    let mut last_n = 0;
+    while boards.len() > 1 {
+        last_n = rng.next().unwrap();
+        for board in &mut boards {
+            board.mark(last_n);
+        }
+        boards.retain(|b| !b.wins());
+    }
+
+    // Only one board remains, play until it wins
+    let board = &mut boards[0];
+    while !board.wins() {
+        last_n = rng.next().unwrap();
+        board.mark(last_n);
+    }
+    println!("{}", board);
+
+    board.score(last_n)
+}
+
+#[derive(Debug)]
+struct Board {
+    nums: [u32; 25],
+    marked: [bool; 25],
+}
+
+impl Board {
+    fn mark(&mut self, n: u32) {
+        for i in 0..25 {
+            if self.nums[i] == n {
+                self.marked[i] = true;
+            }
+        }
+    }
+
+    fn score(&self, last_n: u32) -> u32 {
+        let sum: u32 = self
+            .nums
+            .iter()
+            .zip(self.marked.iter())
+            .filter(|(_, &marked)| !marked)
+            .map(|(n, _)| n)
+            .sum();
+        sum * last_n
+    }
+
+    fn wins(&self) -> bool {
+        // Check rows
+        for row in 0..5 {
+            let mut win = true;
+            for col in 0..5 {
+                if !self.marked[row * 5 + col] {
+                    win = false;
+                    break;
+                }
+            }
+            if win {
+                return true;
+            }
+        }
+        // Check cols
+        for col in 0..5 {
+            let mut win = true;
+            for row in 0..5 {
+                if !self.marked[row * 5 + col] {
+                    win = false;
+                    break;
+                }
+            }
+            if win {
+                return true;
+            }
+        }
+        false
+    }
+}
+
+impl Display for Board {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        for row in 0..5 {
+            for col in 0..5 {
+                let idx = row * 5 + col;
+                write!(
+                    f,
+                    "{}{:02} ",
+                    if self.marked[idx] { "*" } else { " " },
+                    self.nums[idx]
+                )?;
+            }
+            writeln!(f)?;
+        }
+
+        Ok(())
+    }
+}
+
+// Return a list of boards and an rng
+fn input() -> (Vec<Board>, impl Iterator<Item = u32>) {
+    let mut lines = include_str!("../../input/04.txt").lines();
+
+    let rng = lines.next().unwrap().split(',').map(|n| n.parse().unwrap());
+
+    let lines: Vec<_> = lines.collect();
+
+    let mut boards = Vec::new();
+
+    // Chunks have one empty line and five board lines
+    for board in lines.chunks_exact(6) {
+        let b: Vec<u32> = board
+            .iter()
+            .flat_map(|l| l.split_ascii_whitespace())
+            .map(|n| n.parse().unwrap())
+            .collect();
+        boards.push(Board {
+            nums: b.try_into().unwrap(),
+            marked: [false; 25],
+        })
+    }
+
+    (boards, rng)
+}