From 1a45edd3ff90263e360c67712f197675c975db4c Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Mon, 4 Dec 2023 08:11:27 +0100
Subject: [PATCH] Implement 2023 day 4

---
 2023/benches/days.rs    |   2 +-
 2023/src/day04.rs       | 105 ++++++++++++++++++++++++++++++++++++++--
 2023/src/samples/04.txt |   6 +++
 3 files changed, 108 insertions(+), 5 deletions(-)
 create mode 100644 2023/src/samples/04.txt

diff --git a/2023/benches/days.rs b/2023/benches/days.rs
index 8662026..22d3836 100644
--- a/2023/benches/days.rs
+++ b/2023/benches/days.rs
@@ -9,7 +9,7 @@ use criterion::Criterion;
 use aoc_2023::get_implementation;
 
 /// Number of days we have an implementation to benchmark
-const DAYS_IMPLEMENTED: u8 = 3;
+const DAYS_IMPLEMENTED: u8 = 4;
 
 fn read_input(day: u8) -> std::io::Result<Vec<u8>> {
     let input_path = format!("inputs/{day:02}.txt");
diff --git a/2023/src/day04.rs b/2023/src/day04.rs
index 7c1760f..c335378 100644
--- a/2023/src/day04.rs
+++ b/2023/src/day04.rs
@@ -1,7 +1,104 @@
-pub fn part1(_input: &[u8]) -> anyhow::Result<String> {
-    anyhow::bail!("Not implemented")
+use nom::bytes::complete::tag;
+use nom::character::complete::newline;
+use nom::character::complete::space1;
+use nom::combinator::iterator;
+use nom::combinator::map;
+use nom::multi::fold_many1;
+use nom::multi::many1;
+use nom::sequence::delimited;
+use nom::sequence::pair;
+use nom::sequence::preceded;
+use nom::sequence::tuple;
+use nom::IResult;
+
+use crate::common::convert_nom_error;
+use crate::common::parse_input;
+
+struct Card {
+    have: u128,
+    winning: u128,
 }
 
-pub fn part2(_input: &[u8]) -> anyhow::Result<String> {
-    anyhow::bail!("Not implemented")
+fn parse_card(i: &[u8]) -> IResult<&[u8], Card> {
+    fn parse_set(i: &[u8]) -> IResult<&[u8], u128> {
+        fold_many1(
+            preceded(space1, nom::character::complete::u8),
+            || 0u128,
+            |cur, bit| cur | (1 << bit),
+        )(i)
+    }
+
+    map(
+        pair(
+            preceded(
+                delimited(
+                    pair(tag("Card"), space1),
+                    nom::character::complete::u32,
+                    tag(":"),
+                ),
+                parse_set,
+            ),
+            delimited(tag(" |"), parse_set, newline),
+        ),
+        |(have, winning)| Card { have, winning },
+    )(i)
+}
+
+pub fn part1(input: &[u8]) -> anyhow::Result<String> {
+    let mut card_it = iterator(input, parse_card);
+
+    let total: u32 = card_it
+        .into_iter()
+        .map(|card| {
+            let winners = (card.have & card.winning).count_ones();
+
+            if winners > 0 {
+                1 << winners - 1
+            } else {
+                0
+            }
+        })
+        .sum();
+
+    card_it.finish().map_err(|e| match e {
+        nom::Err::Incomplete(_) => anyhow::anyhow!("unreachable"),
+        nom::Err::Failure(e) | nom::Err::Error(e) => convert_nom_error(e),
+    })?;
+
+    Ok(total.to_string())
+}
+
+pub fn part2(input: &[u8]) -> anyhow::Result<String> {
+    let cards = parse_input(input, many1(parse_card))?;
+    let mut counts = vec![1; cards.len()];
+
+    for (id, card) in cards.iter().enumerate() {
+        let winners = (card.have & card.winning).count_ones() as usize;
+        let count = counts[id];
+
+        for offset in 1..=winners {
+            counts[id + offset] += count;
+        }
+    }
+
+    let total: u32 = counts.iter().sum();
+
+    Ok(total.to_string())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/04.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!(part1(SAMPLE).unwrap(), "13");
+    }
+
+    #[test]
+    fn sample_part2() {
+        assert_eq!(part2(SAMPLE).unwrap(), "30");
+    }
 }
diff --git a/2023/src/samples/04.txt b/2023/src/samples/04.txt
new file mode 100644
index 0000000..9bdb874
--- /dev/null
+++ b/2023/src/samples/04.txt
@@ -0,0 +1,6 @@
+Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53
+Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
+Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1
+Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83
+Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
+Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11