star twenty

src/main.rs

@@ -19,6 +19,7 @@ mod star_sixteen;
 mod star_seventeen;
 mod star_eighteen;
 mod star_nineteen;
+mod star_twenty;
 
 fn main() {
     let args: Vec<String> = env::args().collect();
@@ -42,6 +43,7 @@ fn main() {
         "17" => star_seventeen::run(),
         "18" => star_eighteen::run(),
         "19" => star_nineteen::run(),
+        "20" => star_twenty::run(),
         _ => unreachable!(),
     }
 }

src/star_twenty.rs

@@ -0,0 +1,175 @@
+use std::fs;
+
+pub fn run() {
+    let file = fs::read_to_string("./inputs/star_twenty.txt").unwrap();
+    let (positions, w, h) = parse_input(&file);
+    let result = calculate_total_map_score(&positions, w, h);
+
+    println!("Result: {}", result);
+}
+
+const DIRECTIONS: [(isize, isize); 4] = [
+    (0, -1), // Up
+    (0, 1), // Down
+    (-1, 0), // Left
+    (1, 0), // Right
+];
+
+#[derive(Copy, Clone, PartialEq, Debug, Eq, Hash)]
+struct Position {
+    x: isize,
+    y: isize,
+    h: isize,
+}
+
+fn parse_input(input: &String) -> (Vec<Position>, usize, usize) {
+
+    let w = input.lines().next().unwrap().len();
+    let h = input.lines().count();
+
+    let mut input = input.clone();
+    input.retain(|s| !s.is_whitespace());
+
+    let mut positions = vec![];
+
+    let mut x = 0;
+    let mut y = 0;
+    for found_char in input.chars() {
+        let h = found_char.to_string().parse::<isize>().unwrap();
+        positions.push(Position{x, y, h});
+        x += 1;
+        if x as usize >= w {
+            x = 0;
+            y += 1;
+        }
+    }
+
+    (positions, w, h)
+}
+
+fn calculate_trailhead_score(current_position: &Position, positions: &Vec<Position>, w: usize, h: usize) -> usize {
+    if current_position.h >= 9 {
+        return 1;
+    }
+    let mut count = 0;
+
+    for (index, direction) in DIRECTIONS.iter().enumerate() {
+        if current_position.x <= 0 && index == 2
+            || current_position.x >= (w as isize - 1) && index == 3
+            || current_position.y <= 0 && index == 0
+            || current_position.y >= (h as isize - 1) && index == 1
+        {
+            continue;
+        }
+        let x = (current_position.x + direction.0) as usize;
+        let y = (current_position.y + direction.1) as usize;
+        let new_position = positions[x + (y * w)];
+        if new_position.h == (current_position.h + 1) {
+            count += calculate_trailhead_score(&new_position, positions, w, h);
+        }
+    }
+
+    count
+}
+
+fn calculate_total_map_score(positions: &Vec<Position>, w: usize, h: usize) -> usize {
+    positions.iter()
+        .filter(|p| p.h == 0)
+        .map(|p| calculate_trailhead_score(p, positions, w, h))
+        .sum()
+}
+
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_parse_input() {
+        let input = vec![
+            "0123",
+            "1234",
+            "8765",
+            "9876"
+        ].join("\n");
+        assert_eq!(
+            parse_input(&input),
+            (vec![
+                Position{x: 0, y: 0, h: 0},
+                Position{x: 1, y: 0, h: 1},
+                Position{x: 2, y: 0, h: 2},
+                Position{x: 3, y: 0, h: 3},
+                Position{x: 0, y: 1, h: 1},
+                Position{x: 1, y: 1, h: 2},
+                Position{x: 2, y: 1, h: 3},
+                Position{x: 3, y: 1, h: 4},
+                Position{x: 0, y: 2, h: 8},
+                Position{x: 1, y: 2, h: 7},
+                Position{x: 2, y: 2, h: 6},
+                Position{x: 3, y: 2, h: 5},
+                Position{x: 0, y: 3, h: 9},
+                Position{x: 1, y: 3, h: 8},
+                Position{x: 2, y: 3, h: 7},
+                Position{x: 3, y: 3, h: 6},
+            ], 4, 4),
+        );
+    }
+
+    #[test]
+    fn test_calculate_trailhead_score() {
+        let input = vec![
+            "0000000",
+            "0043210",
+            "0050020",
+            "0065430",
+            "0070040",
+            "0087650",
+            "0090000"
+        ].join("\n");
+        let (positions, w, h) = parse_input(&input);
+        let current_position = Position{x: 5, y: 0, h: 0};
+        assert_eq!(calculate_trailhead_score(&current_position, &positions, w, h), 3);
+
+        let input = vec![
+            "0090009",
+            "0001098",
+            "0002007",
+            "6543456",
+            "7650987",
+            "8760000",
+            "9870000"
+        ].join("\n");
+        let (positions, w, h) = parse_input(&input);
+        let current_position = Position{x: 3, y: 0, h: 0};
+        assert_eq!(calculate_trailhead_score(&current_position, &positions, w, h), 13);
+
+        let input = vec![
+            "012345",
+            "123456",
+            "234567",
+            "345678",
+            "406789",
+            "567890",
+        ].join("\n");
+        let (positions, w, h) = parse_input(&input);
+        let current_position = Position{x: 0, y: 0, h: 0};
+        assert_eq!(calculate_trailhead_score(&current_position, &positions, w, h), 227);
+    }
+
+    #[test]
+    fn test_calculate_total_map_score() {
+        let input = vec![
+            "89010123",
+            "78121874",
+            "87430965",
+            "96549874",
+            "45678903",
+            "32019012",
+            "01329801",
+            "10456732"
+        ].join("\n");
+        let (positions, w, h) = parse_input(&input);
+        assert_eq!(calculate_total_map_score(&positions, w, h), 81);
+    }
+}