Use iterator instead of range

By working with binary numbers as integers rather than byte strings, we
don't need to allocate a Vec for each of them, reducing us to just the
allocations in the outer Vec.

2021/inputs/04.txt

@@ -0,0 +1,601 @@
+23,91,18,32,73,14,20,4,10,55,40,29,13,25,48,65,2,80,22,16,93,85,66,21,9,36,47,72,88,58,5,42,53,69,52,8,54,63,76,12,6,99,35,95,82,49,41,17,62,34,51,77,94,7,28,71,92,74,46,79,26,19,97,86,87,37,57,64,1,30,11,96,70,44,83,0,56,90,59,78,61,98,89,43,3,84,67,38,68,27,81,39,15,50,60,24,45,75,33,31
+
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+
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2021/src/day03.rs

@@ -42,44 +42,41 @@ pub fn part1(input: &mut dyn Read) -> String {
     (gamma * epsilon).to_string()
 }
 
-fn find_remaining(mut strings: Vec<Vec<u8>>, most: bool) -> u32 {
+fn find_remaining(mut strings: Vec<u32>, most: bool, len: usize) -> u32 {
-    let comp: fn(usize, usize) -> bool = if most {
+    for pos in 1..=len {
-        |occurrences, len| occurrences * 2 >= len
-    } else {
-        |occurrences, len| occurrences * 2 < len
-    };
-
-    for pos in 0..strings[0].len() {
         if strings.len() == 1 {
             break;
         }
 
-        let occurrences = strings.iter().filter(|b| b[pos] == b'1').count();
+        let bit = 1 << (len - pos);
 
-        let keep = if comp(occurrences, strings.len()) {
+        let occurrences = strings.iter().filter(|&&b| (b & bit) == bit).count();
-            b'1'
+
+        let keep = if (occurrences * 2 < strings.len()) ^ most {
+            bit
         } else {
-            b'0'
+            0
         };
 
-        strings.retain(|s| s[pos] == keep);
+        strings.retain(|&b| (b & bit) == keep);
     }
 
     strings[0]
-        .iter()
-        .fold(0, |n, &b| (n << 1) | (b - b'0') as u32)
 }
 
 pub fn part2(input: &mut dyn Read) -> String {
     let mut strings = Vec::new();
     let mut reader = LineIter::new(input);
+    let mut read_line = reader.next();
+    let len = read_line.unwrap().len();
 
-    while let Some(line) = reader.next() {
+    while let Some(line) = read_line {
-        strings.push(line.as_bytes().to_owned());
+        strings.push(u32::from_str_radix(line, 2).unwrap());
+        read_line = reader.next();
     }
 
-    let oxygen = find_remaining(strings.clone(), true);
+    let oxygen = find_remaining(strings.clone(), true, len);
-    let co2 = find_remaining(strings, false);
+    let co2 = find_remaining(strings, false, len);
 
     (oxygen * co2).to_string()
 }

2021/src/day04.rs

@@ -1,9 +1,139 @@
+use std::collections::HashMap;
 use std::io::Read;
 
-pub fn part1(_input: &mut dyn Read) -> String {
+use crate::common::LineIter;
-    todo!()
+
+#[derive(Debug)]
+struct BingoCard {
+    ticks: [[bool; 5]; 5],
+    mapping: HashMap<u8, (u8, u8)>,
 }
 
-pub fn part2(_input: &mut dyn Read) -> String {
+impl BingoCard {
-    todo!()
+    pub fn cross(&mut self, num: u8) -> bool {
+        if let Some(&(x, y)) = self.mapping.get(&num) {
+            self.ticks[y as usize][x as usize] = true;
+            true
+        } else {
+            false
+        }
+    }
+
+    pub fn has_won(&self) -> bool {
+        // Check horizontal lines
+        if self.ticks.iter().any(|s| s.iter().all(|&b| b)) {
+            return true;
+        }
+
+        // Check vertical lines
+        (0..5).any(|x| self.ticks.iter().all(|row| row[x]))
+
+        // Diagonals do not count
+    }
+
+    pub fn remaining(&self) -> u32 {
+        self.mapping
+            .iter()
+            .filter_map(|(&num, &(x, y))| {
+                if self.ticks[y as usize][x as usize] {
+                    None
+                } else {
+                    Some(num as u32)
+                }
+            })
+            .sum()
+    }
+}
+
+fn read_input(input: &mut dyn Read) -> (Vec<u8>, Vec<BingoCard>) {
+    let mut reader = LineIter::new(input);
+
+    let numbers: Vec<u8> = reader
+        .next()
+        .unwrap()
+        .split(',')
+        .map(|num| num.parse().unwrap())
+        .collect();
+
+    let mut bingo_cards = Vec::new();
+
+    while reader.next().is_some() {
+        let mut mapping = HashMap::with_capacity(25);
+
+        for y in 0..5 {
+            reader
+                .next()
+                .unwrap()
+                .split(' ')
+                .filter_map(|s| if s.is_empty() { None } else { s.parse().ok() })
+                .enumerate()
+                .for_each(|(x, num)| {
+                    mapping.insert(num, (x as u8, y));
+                });
+        }
+
+        let card = BingoCard {
+            mapping,
+            ticks: Default::default(),
+        };
+
+        bingo_cards.push(card);
+    }
+
+    (numbers, bingo_cards)
+}
+
+pub fn part1(input: &mut dyn Read) -> String {
+    let (numbers, mut bingo_cards) = read_input(input);
+
+    for number in numbers {
+        for card in &mut bingo_cards {
+            if card.cross(number) && card.has_won() {
+                return (number as u32 * card.remaining()).to_string();
+            }
+        }
+    }
+
+    panic!("None of the cards won")
+}
+
+pub fn part2(input: &mut dyn Read) -> String {
+    let (numbers, mut bingo_cards) = read_input(input);
+    let mut bingo_won = vec![false; bingo_cards.len()];
+    let mut num_won = 0;
+    let to_win = bingo_cards.len();
+
+    for num in numbers {
+        for (won, card) in bingo_won.iter_mut().zip(bingo_cards.iter_mut()) {
+            if !*won && card.cross(num) && card.has_won() {
+                *won = true;
+                num_won += 1;
+
+                if num_won == to_win {
+                    return (num as u32 * card.remaining()).to_string();
+                }
+            }
+        }
+    }
+
+    panic!("Not all cards won!")
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::test_implementation;
+
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/04.txt");
+
+    #[test]
+    fn sample_part1() {
+        test_implementation(part1, SAMPLE, 4512)
+    }
+
+    #[test]
+    fn sample_part2() {
+        test_implementation(part2, SAMPLE, 1924)
+    }
 }

2021/src/samples/04.txt

@@ -0,0 +1,19 @@
+7,4,9,5,11,17,23,2,0,14,21,24,10,16,13,6,15,25,12,22,18,20,8,19,3,26,1
+
+22 13 17 11  0
+ 8  2 23  4 24
+21  9 14 16  7
+ 6 10  3 18  5
+ 1 12 20 15 19
+
+ 3 15  0  2 22
+ 9 18 13 17  5
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+20 11 10 24  4
+14 21 16 12  6
+
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+10 16 15  9 19
+18  8 23 26 20
+22 11 13  6  5
+ 2  0 12  3  7