From 4183f4a242bc9069a10f6278aa82326c9722552e Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Wed, 6 Dec 2023 08:29:41 +0100
Subject: [PATCH] Implement 2023 day 6 part 1

---
 2023/src/day06.rs       | 56 +++++++++++++++++++++++++++++++++++++++--
 2023/src/samples/06.txt |  2 ++
 2 files changed, 56 insertions(+), 2 deletions(-)
 create mode 100644 2023/src/samples/06.txt

diff --git a/2023/src/day06.rs b/2023/src/day06.rs
index 7c1760f..16e44fc 100644
--- a/2023/src/day06.rs
+++ b/2023/src/day06.rs
@@ -1,7 +1,59 @@
-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::multi::many1;
+use nom::sequence::delimited;
+use nom::sequence::pair;
+use nom::sequence::preceded;
+use nom::IResult;
+
+use crate::common::parse_input;
+
+fn parse_race(i: &[u8]) -> IResult<&[u8], (Vec<u64>, Vec<u64>)> {
+    use nom::character::complete::u64;
+
+    pair(
+        delimited(tag("Time:"), many1(preceded(space1, u64)), newline),
+        delimited(tag("Distance:"), many1(preceded(space1, u64)), newline),
+    )(i)
+}
+
+fn ways(time: u64, distance: u64) -> u64 {
+    let make_it = (1..=time / 2)
+        .filter(|&v| v * (time - v) > distance)
+        .count() as u64;
+
+    if time % 2 == 0 {
+        2 * make_it - 1
+    } else {
+        2 * make_it
+    }
+}
+
+pub fn part1(input: &[u8]) -> anyhow::Result<String> {
+    let (time, distance) = parse_input(input, parse_race)?;
+
+    let total: u64 = time
+        .iter()
+        .zip(&distance)
+        .map(|(&time, &distance)| ways(time, distance))
+        .product();
+
+    Ok(total.to_string())
 }
 
 pub fn part2(_input: &[u8]) -> anyhow::Result<String> {
     anyhow::bail!("Not implemented")
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/06.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!(part1(SAMPLE).unwrap(), "288");
+    }
+}
diff --git a/2023/src/samples/06.txt b/2023/src/samples/06.txt
new file mode 100644
index 0000000..28f5ae9
--- /dev/null
+++ b/2023/src/samples/06.txt
@@ -0,0 +1,2 @@
+Time:      7  15   30
+Distance:  9  40  200