From 8d42f5a41537fd599600b0246358843f83d9664f Mon Sep 17 00:00:00 2001
From: Daniel Lin <ephemient@gmail.com>
Date: Sat, 7 Dec 2024 03:57:40 -0500
Subject: [PATCH] Day 7: Bridge Repair

---
 README.md               |  2 +-
 rs/benches/criterion.rs |  8 +++-
 rs/src/day7.rs          | 95 +++++++++++++++++++++++++++++++++++++++++
 rs/src/lib.rs           |  1 +
 rs/src/main.rs          | 10 ++++-
 5 files changed, 113 insertions(+), 3 deletions(-)
 create mode 100644 rs/src/day7.rs

diff --git a/README.md b/README.md
index f3aaf501..f00e79b3 100644
--- a/README.md
+++ b/README.md
@@ -11,4 +11,4 @@ Development occurs in language-specific directories:
 |[Day4.hs](hs/src/Day4.hs)|[Day4.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day4.kt)|[day4.py](py/aoc2024/day4.py)|[day4.rs](rs/src/day4.rs)|
 |[Day5.hs](hs/src/Day5.hs)|[Day5.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day5.kt)|[day5.py](py/aoc2024/day5.py)|[day5.rs](rs/src/day5.rs)|
 |[Day6.hs](hs/src/Day6.hs)|[Day6.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day6.kt)|[day6.py](py/aoc2024/day6.py)|[day6.rs](rs/src/day6.rs)|
-|[Day7.hs](hs/src/Day7.hs)|[Day7.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day7.kt)|[day7.py](py/aoc2024/day7.py)||
+|[Day7.hs](hs/src/Day7.hs)|[Day7.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day7.kt)|[day7.py](py/aoc2024/day7.py)|[day7.rs](rs/src/day7.rs)|
diff --git a/rs/benches/criterion.rs b/rs/benches/criterion.rs
index 72292072..d946b4d9 100644
--- a/rs/benches/criterion.rs
+++ b/rs/benches/criterion.rs
@@ -1,4 +1,4 @@
-use aoc2024::{day1, day2, day3, day4, day5, day6};
+use aoc2024::{day1, day2, day3, day4, day5, day6, day7};
 use criterion::{black_box, Criterion};
 use std::env;
 use std::fs;
@@ -50,6 +50,12 @@ fn aoc2024_bench(c: &mut Criterion) -> io::Result<()> {
     g.bench_function("part 2", |b| b.iter(|| day6::part2(black_box(&data))));
     g.finish();
 
+    let data = get_day_input(7)?;
+    let mut g = c.benchmark_group("day 7");
+    g.bench_function("part 1", |b| b.iter(|| day7::part1(black_box(&data))));
+    g.bench_function("part 2", |b| b.iter(|| day7::part2(black_box(&data))));
+    g.finish();
+
     Ok(())
 }
 
diff --git a/rs/src/day7.rs b/rs/src/day7.rs
new file mode 100644
index 00000000..0b4b9b19
--- /dev/null
+++ b/rs/src/day7.rs
@@ -0,0 +1,95 @@
+fn solve<F, I>(data: &str, op: F) -> usize
+where
+    F: Fn(usize, usize) -> I,
+    I: IntoIterator<Item = usize>,
+{
+    data.lines()
+        .filter_map(|line| {
+            let (lhs, rhs) = line.split_once(": ")?;
+            let lhs = lhs.parse::<usize>().ok()?;
+            let rhs = rhs
+                .split_ascii_whitespace()
+                .map(|value| value.parse())
+                .collect::<Result<Vec<_>, _>>()
+                .ok()?;
+            let mut stack = vec![(lhs, rhs)];
+            while let Some((x, mut rest)) = stack.pop() {
+                let y = rest.pop()?;
+                if rest.is_empty() {
+                    if x == y {
+                        return Some(lhs);
+                    }
+                    continue;
+                }
+                for z in op(x, y) {
+                    stack.push((z, rest.clone()));
+                }
+            }
+            None
+        })
+        .sum()
+}
+
+pub fn part1(data: &str) -> usize {
+    solve(data, |x, y| {
+        let mut values = vec![];
+        if let Some(z) = x.checked_sub(y) {
+            values.push(z);
+        }
+        if x % y == 0 {
+            values.push(x / y);
+        }
+        values
+    })
+}
+
+pub fn part2(data: &str) -> usize {
+    solve(data, |x, y| {
+        let mut values = vec![];
+        if let Some(z) = x.checked_sub(y) {
+            values.push(z);
+        }
+        if x % y == 0 {
+            values.push(x / y);
+        }
+        if x > y {
+            let mut d = 10;
+            while d <= y {
+                d *= 10;
+            }
+            if x % d == y {
+                values.push(x / d);
+            }
+        }
+        values
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE: &str = indoc! {"
+        190: 10 19
+        3267: 81 40 27
+        83: 17 5
+        156: 15 6
+        7290: 6 8 6 15
+        161011: 16 10 13
+        192: 17 8 14
+        21037: 9 7 18 13
+        292: 11 6 16 20
+    "};
+
+    #[test]
+    fn part1_examples() {
+        assert_eq!(3749, part1(EXAMPLE));
+    }
+
+    #[test]
+    fn part2_examples() {
+        assert_eq!(11387, part2(EXAMPLE));
+    }
+}
diff --git a/rs/src/lib.rs b/rs/src/lib.rs
index d52973ba..da2f9142 100644
--- a/rs/src/lib.rs
+++ b/rs/src/lib.rs
@@ -4,3 +4,4 @@ pub mod day3;
 pub mod day4;
 pub mod day5;
 pub mod day6;
+pub mod day7;
diff --git a/rs/src/main.rs b/rs/src/main.rs
index 93c985f8..0c506941 100644
--- a/rs/src/main.rs
+++ b/rs/src/main.rs
@@ -1,5 +1,5 @@
 use anyhow::anyhow;
-use aoc2024::{day1, day2, day3, day4, day5, day6};
+use aoc2024::{day1, day2, day3, day4, day5, day6, day7};
 use std::collections::HashSet;
 use std::env;
 use std::fs;
@@ -65,5 +65,13 @@ fn main() -> anyhow::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("7") {
+        println!("Day 7");
+        let data = get_day_input(7)?;
+        println!("{:?}", day7::part1(&data));
+        println!("{:?}", day7::part2(&data));
+        println!();
+    }
+
     Ok(())
 }