Day 13

13-shuttle_search/Cargo.lock

@@ -0,0 +1,75 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "anyhow"
+version = "1.0.38"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "afddf7f520a80dbf76e6f50a35bca42a2331ef227a28b3b6dc5c2e2338d114b1"
+
+[[package]]
+name = "chinese_remainder"
+version = "0.1.0"
+
+[[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 = "1.0.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "991431c3519a3f36861882da93630ce66b52918dcf1b8e2fd66b397fc96f28df"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "shuttle_search"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "chinese_remainder",
+ "thiserror",
+]
+
+[[package]]
+name = "syn"
+version = "1.0.60"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c700597eca8a5a762beb35753ef6b94df201c81cca676604f547495a0d7f0081"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-xid",
+]
+
+[[package]]
+name = "thiserror"
+version = "1.0.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "76cc616c6abf8c8928e2fdcc0dbfab37175edd8fb49a4641066ad1364fdab146"
+dependencies = [
+ "thiserror-impl",
+]
+
+[[package]]
+name = "thiserror-impl"
+version = "1.0.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9be73a2caec27583d0046ef3796c3794f868a5bc813db689eed00c7631275cd1"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "unicode-xid"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f7fe0bb3479651439c9112f72b6c505038574c9fbb575ed1bf3b797fa39dd564"

13-shuttle_search/Cargo.toml

@@ -7,3 +7,6 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+anyhow = "1.0.38"
+chinese_remainder = { path = "../chinese_remainder/" }
+thiserror = "1.0.23"

13-shuttle_search/data/input.txt

@@ -0,0 +1,2 @@
+1014511
+17,x,x,x,x,x,x,41,x,x,x,x,x,x,x,x,x,643,x,x,x,x,x,x,x,23,x,x,x,x,13,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,29,x,433,x,x,x,x,x,37,x,x,x,x,x,x,x,x,x,x,x,x,19

13-shuttle_search/src/main.rs

@@ -1,3 +1,97 @@
-fn main() {
+use anyhow::Result;
-    println!("Hello, world!");
+
+#[derive(Debug, PartialEq)]
+struct ProblemStatement {
+    departure: u64,
+    lines: Vec<u64>,
+}
+fn main() {
+    let input = include_str!("../data/input.txt");
+    println!("Part 1: {}", step1(parse_input(input).unwrap()));
+    println!("Part 2: {}", step2(input));
+}
+
+fn parse_input(i: &str) -> Result<ProblemStatement> {
+    let mut lines = i.lines();
+    Ok(ProblemStatement {
+        departure: lines
+            .next()
+            .ok_or_else(|| anyhow::anyhow!("Missing departure"))?
+            .parse::<u64>()?,
+        lines: lines
+            .next()
+            .unwrap()
+            .split(',')
+            .filter(|&c| c != "x")
+            .map(|t| t.parse::<u64>().unwrap())
+            .collect(),
+    })
+}
+
+fn step1(p: ProblemStatement) -> u64 {
+    let r = p
+        .lines
+        .iter()
+        .map(|&l| (l - p.departure % l, l))
+        .min()
+        .unwrap();
+    r.0 * r.1
+}
+
+fn step2(input: &str) -> i64 {
+    let (remainders, moduli): (Vec<i64>, Vec<i64>) = input.lines().nth(1)
+        .unwrap()
+        .split(',')
+        .enumerate()
+        .filter_map(
+            |(num, lineno)| {
+                let line = str::parse::<i64>(lineno).ok()?;
+                Some((line - num as i64, line))
+            }
+        )
+        .unzip();
+    chinese_remainder::chinese_remainder(&remainders, &moduli).unwrap()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    static INPUT: &str = r#"939
+7,13,x,x,59,x,31,19"#;
+
+    #[test]
+    fn test_parse() {
+        assert_eq!(
+            parse_input(INPUT).unwrap(),
+            ProblemStatement {
+                departure: 939,
+                lines: vec![7, 13, 59, 31, 19],
+            }
+        )
+    }
+
+    #[test]
+    fn test_step1() {
+        assert_eq!(step1(parse_input(INPUT).unwrap()), 295)
+    }
+
+    #[test]
+    fn test_step2() {
+        let v_rep = vec![
+            (INPUT, 1068781),
+            ("0\n17,x,13,19", 3417),
+            ("0\n67,7,59,61", 754018),
+            ("0\n67,x,7,59,61", 779210),
+            ("0\n67,7,x,59,61", 1261476),
+            ("0\n1789,37,47,1889", 1202161486),
+        ];
+        assert_eq!(
+            v_rep
+                .iter()
+                .map(|(i, _)| (*i, step2(i)))
+                .collect::<Vec<_>>(),
+            v_rep,
+        )
+    }
 }

chinese_remainder/Cargo.lock

@@ -0,0 +1,5 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "chinese_remainder"
+version = "0.1.0"

chinese_remainder/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "chinese_remainder"
+version = "0.1.0"
+authors = ["Guilhem MARION <gmarion@netc.fr>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

chinese_remainder/src/lib.rs

@@ -0,0 +1,64 @@
+/// Represents the GCD computed as part of the Extended Euclidean Algorithm.
+/// This invariant should always be valid : ax + by = gcd
+#[derive(Debug,PartialEq)]
+pub struct EGCD {
+    pub a: i64,
+    pub b: i64,
+    pub x: i64,
+    pub y: i64,
+    pub gcd: i64,
+}
+
+/// Computes the Extended Euclidean Algorithm's solution to finding a & b's GCD
+/// Additionally to the standard Euclidean Algorithm, it provides x and y so
+/// that ax + by = GCD
+pub fn egcd(a: i64, b: i64) -> EGCD {
+    // If b == 0, then a == gcd(a,b)
+    // Then gcd = 1 * a + 0 * b follows
+    if b == 0 {
+        EGCD {
+            a,
+            b,
+            x: 1,
+            // Anything other than 0 gives a valid solution but
+            // With different end x and y
+            y: 0,
+            gcd: a,
+        }
+    } else {
+        let rec = egcd(b, a%b);
+        EGCD {
+            a,
+            b,
+            x: rec.y,
+            y: rec.x - rec.y * (a / b),
+            gcd: rec.gcd,
+        }
+    }
+}
+
+/// Solves the chinese remainder problem, stated as follows:
+/// ```noexec
+/// for i in residues.len(),
+///     (chinese_remainder(residues, moduli) - residues[i]) / moduli[i] == 0
+/// ``` 
+pub fn chinese_remainder(residues: &[i64], moduli: &[i64]) -> Option<i64> {
+    // TODO: Filter out 0s in moduli (meaning big_n is 0 -> div by 0)
+    let big_n: i64 = moduli.iter().product();
+    Some(moduli.iter()
+        .map(|&ni| {
+            egcd(ni, big_n / ni)
+        })
+        .zip(residues)
+        .map(|(egcd,ai)| {
+            if egcd.gcd != 1 {
+                // Fail in case moduli are not co-prime
+                None
+            } else {
+                Some(ai * egcd.y * egcd.b)
+            }
+        })
+        .sum::<Option<i64>>()?
+        .rem_euclid(big_n)) // Sum on Option<_> returns None if the Iter
+                            // contains a None
+}

chinese_remainder/tests/tests.rs

@@ -0,0 +1,36 @@
+#[cfg(test)]
+mod tests {
+    use chinese_remainder::{EGCD, egcd, chinese_remainder};
+
+    #[test]
+    fn test_egcd() {
+        assert_eq!(
+            egcd(25, 7),
+            EGCD {
+                a: 25,
+                b: 7,
+                x: 2,
+                y: -7,
+                gcd: 1,
+            }
+        )
+    }
+    #[test]
+    fn test_cr1() {
+        assert_eq!(
+            chinese_remainder(&[2, 3, 2], &[3, 5, 7]), Some(23));
+    }
+
+    #[test]
+    fn test_cr2() {
+        assert_eq!(
+            chinese_remainder(&[11,22,19], &[10,4,9]), None);
+    }
+
+    #[test]
+    fn test_cr3() {
+        assert_eq!(
+            chinese_remainder(&[10,4,12], &[11,12,13]), Some(1000));
+    }
+
+}