day 1

.gitignore

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+/target
+/input

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "aoc2024"
+version = "0.1.0"
+dependencies = [
+ "thiserror",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.92"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "37d3544b3f2748c54e147655edb5025752e2303145b5aefb3c3ea2c78b973bb0"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.37"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b5b9d34b8991d19d98081b46eacdd8eb58c6f2b201139f7c5f643cc155a633af"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "syn"
+version = "2.0.90"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "919d3b74a5dd0ccd15aeb8f93e7006bd9e14c295087c9896a110f490752bcf31"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "thiserror"
+version = "2.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c006c85c7651b3cf2ada4584faa36773bd07bac24acfb39f3c431b36d7e667aa"
+dependencies = [
+ "thiserror-impl",
+]
+
+[[package]]
+name = "thiserror-impl"
+version = "2.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f077553d607adc1caf65430528a576c757a71ed73944b66ebb58ef2bbd243568"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "adb9e6ca4f869e1180728b7950e35922a7fc6397f7b641499e8f3ef06e50dc83"

Cargo.toml

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+[package]
+    edition = "2021"
+    name    = "aoc2024"
+    version = "0.1.0"
+
+[dependencies]
+    thiserror = "2"

src/lib.rs

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+pub mod solutions;

src/main.rs

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+use aoc2024::solutions::day_1::part_two;
+
+fn main() {
+    println!("{}", part_two());
+}

src/solutions/day_1.rs

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+use std::collections::HashMap;
+
+const INPUT: &str = include_str!("../../input/day1.txt");
+
+pub fn part_one() -> u64 {
+    let (mut left, mut right) = INPUT
+        .lines()
+        .filter_map(|s| s.split_once(' ').map(|(s, x)| (s.trim(), x.trim())))
+        .filter_map(
+            |(s, x)| match (s.parse::<u64>().ok(), x.parse::<u64>().ok()) {
+                (Some(x), Some(y)) => Some((x, y)),
+                _ => None,
+            },
+        )
+        .fold((Vec::new(), Vec::new()), |(mut v1, mut v2), (x, y)| {
+            v1.push(x);
+            v2.push(y);
+            (v1, v2)
+        });
+
+    left.sort();
+    right.sort();
+
+    left.into_iter()
+        .zip(right)
+        .map(|(l, r)| if l > r { l - r } else { r - l })
+        .sum()
+}
+
+pub fn part_two() -> u64 {
+    let mut cache = HashMap::<u64, u64>::new();
+    let mut similarity_score = 0;
+
+    let (left, right) = INPUT
+        .lines()
+        .filter_map(|s| s.split_once(' ').map(|(s, x)| (s.trim(), x.trim())))
+        .filter_map(
+            |(s, x)| match (s.parse::<u64>().ok(), x.parse::<u64>().ok()) {
+                (Some(x), Some(y)) => Some((x, y)),
+                _ => None,
+            },
+        )
+        .fold((Vec::new(), Vec::new()), |(mut v1, mut v2), (x, y)| {
+            v1.push(x);
+            v2.push(y);
+            (v1, v2)
+        });
+
+    for key in left {
+        if let Some(&val) = cache.get(&key) {
+            similarity_score += key * val;
+        } else {
+            let val = right.iter().filter(|e| e.eq(&&key)).count() as u64;
+            cache.insert(key, val);
+            similarity_score += key * val;
+        }
+    }
+
+    similarity_score
+}

src/solutions/mod.rs

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+pub mod day_1;