day-9/.gitignore

@@ -0,0 +1 @@
+/target/

day-9/Cargo.lock

@@ -0,0 +1,94 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "day-9"
+version = "0.1.0"
+dependencies = [
+ "indoc",
+ "itertools",
+]
+
+[[package]]
+name = "either"
+version = "1.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e78d4f1cc4ae33bbfc157ed5d5a5ef3bc29227303d595861deb238fcec4e9457"
+
+[[package]]
+name = "indoc"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47741a8bc60fb26eb8d6e0238bbb26d8575ff623fdc97b1a2c00c050b9684ed8"
+dependencies = [
+ "indoc-impl",
+ "proc-macro-hack",
+]
+
+[[package]]
+name = "indoc-impl"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ce046d161f000fffde5f432a0d034d0341dc152643b2598ed5bfce44c4f3a8f0"
+dependencies = [
+ "proc-macro-hack",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "unindent",
+]
+
+[[package]]
+name = "itertools"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "284f18f85651fe11e8a991b2adb42cb078325c996ed026d994719efcfca1d54b"
+dependencies = [
+ "either",
+]
+
+[[package]]
+name = "proc-macro-hack"
+version = "0.5.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dbf0c48bc1d91375ae5c3cd81e3722dff1abcf81a30960240640d223f59fe0e5"
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.24"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e0704ee1a7e00d7bb417d0770ea303c1bccbabf0ef1667dae92b5967f5f8a71"
+dependencies = [
+ "unicode-xid",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aa563d17ecb180e500da1cfd2b028310ac758de548efdd203e18f283af693f37"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "syn"
+version = "1.0.54"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9a2af957a63d6bd42255c359c93d9bfdb97076bd3b820897ce55ffbfbf107f44"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-xid",
+]
+
+[[package]]
+name = "unicode-xid"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f7fe0bb3479651439c9112f72b6c505038574c9fbb575ed1bf3b797fa39dd564"
+
+[[package]]
+name = "unindent"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f14ee04d9415b52b3aeab06258a3f07093182b88ba0f9b8d203f211a7a7d41c7"

day-9/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "day-9"
+version = "0.1.0"
+authors = ["Tristan Daniël Maat <tm@tlater.net>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+indoc = "0.3"
+itertools = "0.9"

day-9/src/main.rs

@@ -0,0 +1,134 @@
+use std::fs;
+use std::num::ParseIntError;
+
+use itertools::{Itertools, MinMaxResult};
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("input")?;
+    let xmas = parse_xmas(&input)?;
+
+    // Part 1
+    let result = find_not_summed(&xmas, 25)?;
+    println!("{}", result);
+
+    // Part 2
+    let result = find_weakness(&xmas, result)?;
+    println!("{}", result);
+
+    Ok(())
+}
+
+fn parse_xmas(input: &str) -> Result<Vec<u64>, ParseIntError> {
+    input.lines().map(|line| line.parse()).collect()
+}
+
+fn find_weakness(xmas: &Vec<u64>, key: u64) -> Result<u64, &str> {
+    // Now we use the key to find the weakness, by getting all
+    // possible sub-sumbs of the list of numbers, and finding the one
+    // that happens to match our key
+    let weak_window = (2..xmas.len())
+        .find_map(|window_size| {
+            xmas.windows(window_size)
+                .find(|window| window.iter().sum::<u64>() == key)
+        })
+        .ok_or("Could not find a weakness")?;
+
+    if let MinMaxResult::MinMax(min, max) = weak_window.iter().minmax() {
+        Ok(min + max)
+    } else {
+        unreachable!("We must have at least two elements due to the window size")
+    }
+}
+
+fn find_not_summed(xmas: &Vec<u64>, window_size: usize) -> Result<u64, &str> {
+    xmas.windows(window_size + 1)
+        .find_map(|window| {
+            if let [preamble @ .., number] = window {
+                // If none of the number combinations in the preamble
+                // sum to the final number, we've got the key!
+                if !preamble
+                    .iter()
+                    .combinations(2)
+                    .any(|combination| combination.into_iter().sum::<u64>() == *number)
+                {
+                    Some(*number)
+                } else {
+                    None
+                }
+            } else {
+                unreachable!("The windows must all have a length of at least 1");
+            }
+        })
+        .ok_or("Could not find the entry")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+
+    #[test]
+    fn test_simple() -> Result<(), Box<dyn std::error::Error>> {
+        let input = indoc!(
+            "35
+             20
+             15
+             25
+             47
+             40
+             62
+             55
+             65
+             95
+             102
+             117
+             150
+             182
+             127
+             219
+             299
+             277
+             309
+             576"
+        );
+
+        let xmas = parse_xmas(input)?;
+        let result = find_not_summed(&xmas, 5)?;
+
+        assert_eq!(result, 127);
+        Ok(())
+    }
+
+    #[test]
+    fn test_simple2() -> Result<(), Box<dyn std::error::Error>> {
+        let input = indoc!(
+            "35
+             20
+             15
+             25
+             47
+             40
+             62
+             55
+             65
+             95
+             102
+             117
+             150
+             182
+             127
+             219
+             299
+             277
+             309
+             576"
+        );
+
+        let xmas = parse_xmas(input)?;
+        let key = find_not_summed(&xmas, 5)?;
+        let result = find_weakness(&xmas, key)?;
+
+        assert_eq!(result, 62);
+        Ok(())
+    }
+}

shell.nix

@@ -8,10 +8,9 @@ with pkgs;
 
 mkShell {
   buildInputs = [
-    rustChannel.rust
+    rust-analyzer # the one from Mozilla is slightly broken https://github.com/mozilla/nixpkgs-mozilla/issues/238
+    (pkgs.latest.rustChannels.stable.rust.override {
+      # extensions = ["rust-src"]; # unneeded because we're using rust-analyzer from nixpkgs
+    })
   ];
-
-  shellHook = ''
-    export RUST_SRC_PATH="${rustChannel.rust-src}/lib/rustlib/src/rust/library"
-  '';
 }