feat: completed day 13

ankjevel · ankjevel · commit 05e22daf8123 · 2020-12-14T09:47:42.000+01:00
diff --git a/README.md b/README.md
@@ -14,7 +14,7 @@
 - [Day 10](https://github.com/ankjevel/adventofcode/tree/2020/day_10) 🌟 🌟
 - [Day 11](https://github.com/ankjevel/adventofcode/tree/2020/day_11) 🌟 🌟
 - [Day 12](https://github.com/ankjevel/adventofcode/tree/2020/day_12) 🌟 🌟
-- [Day 13](#)
+- [Day 13](https://github.com/ankjevel/adventofcode/tree/2020/day_13) 🌟 🌟
 - [Day 14](#)
 - [Day 15](#)
 - [Day 16](#)
diff --git a/day_13/Cargo.toml b/day_13/Cargo.toml
@@ -0,0 +1,15 @@
+[package]
+name = "day_13"
+version = "0.1.0"
+edition = "2018"
+authors = ["Dennis Pettersson <mail@dennispettersson.se>"]
+
+[lib]
+doctest = false
+
+[[bin]]
+name = "day_13"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/day_13/src/chinese_remainder.rs b/day_13/src/chinese_remainder.rs
@@ -0,0 +1,29 @@
+// https://rosettacode.org/wiki/Chinese_remainder_theorem#Rust
+
+fn egcd(a: i64, b: i64) -> (i64, i64, i64) {
+    if a == 0 {
+        (b, 0, 1)
+    } else {
+        let (g, x, y) = egcd(b % a, a);
+        (g, y - (b / a) * x, x)
+    }
+}
+
+fn mod_inv(x: i64, n: i64) -> Option<i64> {
+    let (g, x, _) = egcd(x, n);
+    if g == 1 {
+        Some((x % n + n) % n)
+    } else {
+        None
+    }
+}
+
+pub fn chinese_remainder(residues: &[i64], modulii: &[i64]) -> Option<i64> {
+    let prod = modulii.iter().product::<i64>();
+    let mut sum = 0;
+    for (&residue, &modulus) in residues.iter().zip(modulii) {
+        let p = prod / modulus;
+        sum += residue * mod_inv(p, modulus)? * p
+    }
+    Some(sum % prod)
+}
diff --git a/day_13/src/lib.rs b/day_13/src/lib.rs
@@ -0,0 +1,65 @@
+pub mod chinese_remainder;
+pub mod part_01;
+pub mod part_02;
+
+pub type Input = (u64, Vec<Option<u64>>);
+
+pub fn parse_input(input: &str) -> Input {
+    let mut input = input
+        .lines()
+        .map(str::trim)
+        .filter(|string| !string.is_empty())
+        .map(str::to_owned)
+        .into_iter();
+
+    let earliest = input
+        .next()
+        .unwrap_or("".to_string())
+        .parse::<_>()
+        .unwrap_or(0);
+
+    let busses = input.next().unwrap_or("".to_string());
+    let busses = busses
+        .split(",")
+        .into_iter()
+        .map(|string| {
+            if string == "x" {
+                None
+            } else {
+                Some(string.parse::<_>().unwrap_or(0))
+            }
+        })
+        .collect::<Vec<_>>();
+
+    (earliest, busses)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const EXAMPLE_DATA: &'static str = "
+        939
+        7,13,x,x,59,x,31,19
+    ";
+
+    #[test]
+    fn it_parses_example() {
+        assert_eq!(
+            parse_input(&EXAMPLE_DATA),
+            (
+                939,
+                vec![
+                    Some(7),
+                    Some(13),
+                    None,
+                    None,
+                    Some(59),
+                    None,
+                    Some(31),
+                    Some(19)
+                ]
+            )
+        );
+    }
+}
diff --git a/day_13/src/main.rs b/day_13/src/main.rs
@@ -0,0 +1,12 @@
+use std::io::Result;
+
+use day_13::{parse_input, part_01::main as part_01, part_02::main as part_02};
+
+fn main() -> Result<()> {
+    let input = parse_input(include_str!("../../input/day_13"));
+
+    println!("part_01: {:?}", part_01(&input)?);
+    println!("part_02: {:?}", part_02(&input)?);
+
+    Ok(())
+}
diff --git a/day_13/src/part_01.rs b/day_13/src/part_01.rs
@@ -0,0 +1,39 @@
+use std::io::Result;
+
+use crate::Input;
+
+pub fn main((earliest, busses): &Input) -> Result<u64> {
+    let earliest = *earliest;
+    let busses = busses
+        .iter()
+        .filter(|bus| bus.is_some())
+        .map(|bus| bus.unwrap())
+        .collect::<Vec<_>>();
+
+    let mut result = 0;
+    for timestamp in earliest.. {
+        if let Some(bus_id) = busses.iter().find(|bus_id| timestamp % **bus_id == 0) {
+            result = *bus_id * (timestamp - earliest);
+            break;
+        }
+    }
+    Ok(result)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::parse_input;
+
+    use super::*;
+
+    const EXAMPLE_DATA: &'static str = "
+        939
+        7,13,x,x,59,x,31,19
+    ";
+
+    #[test]
+    fn it_gets_the_example_correct() -> Result<()> {
+        assert_eq!(main(&parse_input(&EXAMPLE_DATA))?, 295);
+        Ok(())
+    }
+}
diff --git a/day_13/src/part_02.rs b/day_13/src/part_02.rs
@@ -0,0 +1,33 @@
+use std::io::Result;
+
+use crate::{chinese_remainder::chinese_remainder, Input};
+
+pub fn main((_, busses): &Input) -> Result<i64> {
+    let busses = busses
+        .iter()
+        .enumerate()
+        .filter(|(_, bus)| bus.is_some())
+        .map(|(i, bus)| (i as i64, bus.unwrap_or(0) as i64))
+        .collect::<Vec<_>>();
+    let mods = busses.iter().map(|&(_, b)| b).collect::<Vec<_>>();
+    let res = busses.iter().map(|&(i, b)| b - i).collect::<Vec<_>>();
+    Ok(chinese_remainder(&res, &mods).unwrap())
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::parse_input;
+
+    use super::*;
+
+    #[test]
+    fn it_gets_the_example_correct() -> Result<()> {
+        assert_eq!(main(&parse_input("0\n7,13,x,x,59,x,31,19"))?, 1068781);
+        assert_eq!(main(&parse_input("0\n17,x,13,19"))?, 3417);
+        assert_eq!(main(&parse_input("0\n67,7,59,61"))?, 754018);
+        assert_eq!(main(&parse_input("0\n67,x,7,59,61"))?, 779210);
+        assert_eq!(main(&parse_input("0\n67,7,x,59,61"))?, 1261476);
+        assert_eq!(main(&parse_input("0\n1789,37,47,1889"))?, 1202161486);
+        Ok(())
+    }
+}
diff --git a/input/day_13 b/input/day_13
@@ -0,0 +1,2 @@
+1001287
+13,x,x,x,x,x,x,37,x,x,x,x,x,461,x,x,x,x,x,x,x,x,x,x,x,x,x,17,x,x,x,x,19,x,x,x,x,x,x,x,x,x,29,x,739,x,x,x,x,x,x,x,x,x,41,x,x,x,x,x,x,x,x,x,x,x,x,23

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	`+1001287`
	`2`	`+13,x,x,x,x,x,x,37,x,x,x,x,x,461,x,x,x,x,x,x,x,x,x,x,x,x,x,17,x,x,x,x,19,x,x,x,x,x,x,x,x,x,29,x,739,x,x,x,x,x,x,x,x,x,41,x,x,x,x,x,x,x,x,x,x,x,x,23`