y2015d9 thank you project euler

y2015/src/bin/d9.rs

@@ -0,0 +1,20 @@
+use std::fs;
+
+use y2015::days::d9;
+
+fn main() {
+    part1();
+    part2();
+}
+
+fn part1() {
+    let root = env!("CARGO_MANIFEST_DIR");
+    let content = fs::read_to_string(format!("{root}/resources/9_input.txt")).unwrap();
+    println!("{}", d9::process_part1(&content));
+}
+
+fn part2() {
+    let root = env!("CARGO_MANIFEST_DIR");
+    let content = fs::read_to_string(format!("{root}/resources/9_input.txt")).unwrap();
+    println!("{}", d9::process_part2(&content));
+}

y2015/src/days/d9.rs

@@ -0,0 +1,125 @@
+use core::panic;
+use std::{
+    collections::{HashMap, HashSet},
+    error::Error,
+};
+
+pub fn process_part1(input: &str) -> u32 {
+    let mut distances = HashMap::new();
+    let mut locations = HashSet::new();
+    input.lines().for_each(|line| {
+        let (direction, distance) = line.split_once(" = ").unwrap();
+        let (from, to) = direction.split_once(" to ").unwrap();
+        let distance = distance.parse::<u32>().unwrap();
+        distances.insert((from.to_string(), to.to_string()), distance);
+        locations.insert(from.to_string());
+        locations.insert(to.to_string());
+    });
+    let locations = locations
+        .iter()
+        .map(|place| place.to_string())
+        .collect::<Vec<String>>();
+    let num_permutations = factorial(locations.len());
+    let mut shortest = u32::MAX;
+    for idx in 1..=num_permutations {
+        let perm = permutation(locations.clone(), idx).unwrap();
+        let route_length = get_route_length(perm, &distances);
+        if route_length < shortest {
+            shortest = route_length;
+        }
+    }
+    shortest
+}
+
+fn get_route_length(route: Vec<String>, distances: &HashMap<(String, String), u32>) -> u32 {
+    route
+        .windows(2)
+        .map(|pair| {
+            let distance = distances.get(&(pair[0].clone(), pair[1].clone()));
+            if let Some(distance) = distance {
+                return distance;
+            }
+            let distance = distances.get(&(pair[1].clone(), pair[0].clone()));
+            if let Some(distance) = distance {
+                return distance;
+            }
+            panic!("Should not happen");
+        })
+        .sum()
+}
+
+fn permutation(mut locations: Vec<String>, nth: usize) -> Result<Vec<String>, Box<dyn Error>> {
+    locations.sort();
+    if nth == 1 {
+        return Ok(locations);
+    }
+    if nth > factorial(locations.len()) || nth == 0 {
+        return Err(Box::from("Out of bounds"));
+    }
+    let mut perm = Vec::new();
+    let num_unique_locations = locations.len();
+    let mut remainder = nth - 1;
+    for idx in 1..=locations.len() {
+        let permutations = remainder / factorial(num_unique_locations - idx);
+        remainder %= factorial(num_unique_locations - idx);
+        perm.push(locations[permutations].clone());
+        locations.remove(permutations);
+    }
+    Ok(perm)
+}
+
+fn factorial(num: usize) -> usize {
+    let mut fact = 1;
+    for n in 1..=num {
+        fact *= n;
+    }
+    fact
+}
+
+pub fn process_part2(input: &str) -> u32 {
+    let mut distances = HashMap::new();
+    let mut locations = HashSet::new();
+    input.lines().for_each(|line| {
+        let (direction, distance) = line.split_once(" = ").unwrap();
+        let (from, to) = direction.split_once(" to ").unwrap();
+        let distance = distance.parse::<u32>().unwrap();
+        distances.insert((from.to_string(), to.to_string()), distance);
+        locations.insert(from.to_string());
+        locations.insert(to.to_string());
+    });
+    let locations = locations
+        .iter()
+        .map(|place| place.to_string())
+        .collect::<Vec<String>>();
+    let num_permutations = factorial(locations.len());
+    let mut longest = 0;
+    for idx in 1..=num_permutations {
+        let perm = permutation(locations.clone(), idx).unwrap();
+        let route_length = get_route_length(perm, &distances);
+        if route_length > longest {
+            longest = route_length;
+        }
+    }
+    longest
+}
+
+#[cfg(test)]
+mod tests_9 {
+    use super::*;
+
+    const INPUT: &str = "London to Dublin = 464
+London to Belfast = 518
+Dublin to Belfast = 141";
+
+    #[test]
+    fn it_works() {
+        let result = process_part1(INPUT);
+        assert_eq!(result, 605);
+    }
+
+    #[test]
+    fn part2() {
+        let result = process_part2(INPUT);
+        assert_eq!(result, 982);
+    }
+}

y2015/src/days/mod.rs

@@ -6,3 +6,4 @@ pub mod d5;
 pub mod d6;
 pub mod d7;
 pub mod d8;
+pub mod d9;