3 files changed, 68 insertions, 0 deletions
diff --git a/2024/07/rust/Cargo.lock b/2024/07/rust/Cargo.lock
new file mode 100644
index 0000000..d1897ed
--- /dev/null
+++ b/2024/07/rust/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "aoc_2024-07"
+version = "0.1.0"
diff --git a/2024/07/rust/Cargo.toml b/2024/07/rust/Cargo.toml
new file mode 100644
index 0000000..c64c1b5
--- /dev/null
+++ b/2024/07/rust/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "aoc_2024-07"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/2024/07/rust/src/main.rs b/2024/07/rust/src/main.rs
new file mode 100644
index 0000000..07fef57
--- /dev/null
+++ b/2024/07/rust/src/main.rs
@@ -0,0 +1,55 @@
+use std::io;
+
+fn main() -> io::Result<()> {
+    let eqns = io::stdin()
+        .lines()
+        .flatten()
+        .collect::<Vec<_>>()
+        .iter()
+        .map(|line| line.split_once(": ").unwrap())
+        .map(|(ans, nums)| {
+            (
+                ans.parse::<u64>().unwrap(),
+                nums.split_whitespace()
+                    .map(|s| s.parse::<u64>().unwrap())
+                    .collect::<Vec<_>>(),
+            )
+        })
+        .collect::<Vec<_>>();
+
+    let silver: u64 = eqns
+        .iter()
+        .filter(|(ans, nums)| calibration(ans, nums, false))
+        .map(|(ans, _)| ans)
+        .sum();
+
+    let gold: u64 = eqns
+        .iter()
+        .filter(|(ans, nums)| calibration(ans, nums, true))
+        .map(|(ans, _)| ans)
+        .sum();
+
+    println!("silver: {silver}");
+    println!("gold: {gold}");
+
+    return Ok(());
+}
+
+fn concat(x: &u64, y: &u64) -> u64 {
+    x * (10u64.pow(y.ilog10() + 1)) + y
+}
+
+fn calibration(want: &u64, nums: &[u64], gold: bool) -> bool {
+    match nums {
+        [] => unreachable!(),
+        [x] => want == x,
+        [x, y, xs @ ..] => {
+            if x > want {
+                return false;
+            }
+            calibration(want, &[&[x + y], xs].concat(), gold) ||
+            calibration(want, &[&[x * y], xs].concat(), gold) ||
+            (gold && calibration(want, &[&[concat(x, y)], xs].concat(), gold) )
+        }
+    }
+}