2015 day 9

2015/src/bin/day9.rs

@@ -0,0 +1,118 @@
+use std::collections::{HashMap, HashSet};
+
+use aoc::input;
+
+type Dists = HashMap<String, HashMap<String, u32>>;
+
+fn main() {
+    let lines = input::read_lines();
+    let mut places: HashSet<String> = HashSet::new();
+    let mut dists: Dists = HashMap::new();
+    for line in lines {
+        let parts = line.split_whitespace().collect::<Vec<&str>>();
+        let from = parts[0];
+        let to = parts[2];
+        let dist = parts[4].parse::<u32>().unwrap();
+        if !dists.contains_key(from) {
+            dists.insert(from.to_string(), HashMap::new());
+        }
+        if !dists.contains_key(to) {
+            dists.insert(to.to_string(), HashMap::new());
+        }
+        dists.get_mut(from).unwrap().insert(to.to_string(), dist);
+        dists.get_mut(to).unwrap().insert(from.to_string(), dist);
+        places.insert(from.to_string());
+        places.insert(to.to_string());
+    }
+    let path_len = places.len();
+
+    // Part 1
+    let mut min: u32 = u32::MAX;
+    for place in &places {
+        let shortest_dist =
+            find_shortest_path(&dists, &places, &mut vec![place.to_owned()], 0, path_len);
+        if shortest_dist < min {
+            min = shortest_dist
+        }
+    }
+    println!("Shortest distance: {}", min);
+
+    // Part 2
+    let mut max: u32 = 0;
+    for place in &places {
+        let longest_dist =
+            find_longest_path(&dists, &places, &mut vec![place.to_owned()], 0, path_len);
+        if longest_dist > max {
+            max = longest_dist
+        }
+    }
+    println!("Longest distance: {}", max);
+}
+
+fn find_shortest_path(
+    dists: &Dists,
+    places: &HashSet<String>,
+    cur_path: &mut Vec<String>,
+    cur_dist: u32,
+    max_places: usize,
+) -> u32 {
+    if cur_path.len() == max_places {
+        return cur_dist;
+    }
+    // get next unexplored places
+    let dists_from_here = dists.get(cur_path.last().unwrap()).unwrap();
+    let mut min: u32 = u32::MAX;
+    for next_place in places {
+        if cur_path.contains(next_place) {
+            continue;
+        }
+        cur_path.push(next_place.to_string());
+        let next_place_dist = dists_from_here.get(next_place).unwrap();
+        let shortest_dist = find_shortest_path(
+            dists,
+            places,
+            cur_path,
+            cur_dist + next_place_dist,
+            max_places,
+        );
+        cur_path.pop();
+        if shortest_dist < min {
+            min = shortest_dist;
+        }
+    }
+    min
+}
+
+fn find_longest_path(
+    dists: &Dists,
+    places: &HashSet<String>,
+    cur_path: &mut Vec<String>,
+    cur_dist: u32,
+    max_places: usize,
+) -> u32 {
+    if cur_path.len() == max_places {
+        return cur_dist;
+    }
+    // get next unexplored places
+    let dists_from_here = dists.get(cur_path.last().unwrap()).unwrap();
+    let mut max: u32 = 0;
+    for next_place in places {
+        if cur_path.contains(next_place) {
+            continue;
+        }
+        cur_path.push(next_place.to_string());
+        let next_place_dist = dists_from_here.get(next_place).unwrap();
+        let longest_dist = find_longest_path(
+            dists,
+            places,
+            cur_path,
+            cur_dist + next_place_dist,
+            max_places,
+        );
+        cur_path.pop();
+        if longest_dist > max {
+            max = longest_dist;
+        }
+    }
+    max
+}