Part 1 of Day 10

inputs/day10

@@ -0,0 +1,34 @@
+#..#....#...#.#..#.......##.#.####
+#......#..#.#..####.....#..#...##.
+.##.......#..#.#....#.#..#.#....#.
+###..#.....###.#....##.....#...#..
+...#.##..#.###.......#....#....###
+.####...##...........##..#..#.##..
+..#...#.#.#.###....#.#...##.....#.
+......#.....#..#...##.#..##.#..###
+...###.#....#..##.#.#.#....#...###
+..#.###.####..###.#.##..#.##.###..
+...##...#.#..##.#............##.##
+....#.##.##.##..#......##.........
+.#..#.#..#.##......##...#.#.#...##
+.##.....#.#.##...#.#.#...#..###...
+#.#.#..##......#...#...#.......#..
+#.......#..#####.###.#..#..#.#.#..
+.#......##......##...#..#..#..###.
+#.#...#..#....##.#....#.##.#....#.
+....#..#....##..#...##..#..#.#.##.
+#.#.#.#.##.#.#..###.......#....###
+...#.#..##....###.####.#..#.#..#..
+#....##..#...##.#.#.........##.#..
+.#....#.#...#.#.........#..#......
+...#..###...#...#.#.#...#.#..##.##
+.####.##.#..#.#.#.#...#.##......#.
+.##....##..#.#.#.......#.....####.
+#.##.##....#...#..#.#..###..#.###.
+...###.#..#.....#.#.#.#....#....#.
+......#...#.........##....#....##.
+.....#.....#..#.##.#.###.#..##....
+.#.....#.#.....#####.....##..#....
+.####.##...#.......####..#....##..
+.#.#.......#......#.##..##.#.#..##
+......##.....##...##.##...##......

src/main.rs

@@ -15,6 +15,8 @@ mod scaffold;
 #[cfg(test)]
 mod spring;
 #[cfg(test)]
+mod station;
+#[cfg(test)]
 mod tractor;
 mod wiremap;
 

src/station.rs

@@ -0,0 +1,154 @@
+use std::fs;
+use std::str;
+
+struct StationMap {
+    data: Vec<bool>,
+    width: usize,
+    height: usize,
+}
+
+impl StationMap {
+    fn new(encoding: &str) -> StationMap {
+        let mut data = vec![];
+        let mut width = 0;
+        let mut height = 0;
+
+        for c in encoding.chars() {
+            match c {
+                '.' => data.push(false),
+                '#' => data.push(true),
+                '\n' if width == 0 => {
+                    width = data.len();
+                    height = 1;
+                }
+                '\n' => height += 1,
+                _  => panic!("Unexpected character: {}", c),
+            }
+        }
+
+        StationMap{ data, width, height }
+    }
+
+    fn get(&self, x: usize, y: usize) -> bool {
+        self.data[ (y * self.width) + x ]
+    }
+
+    fn count_visible(&self, from_x: usize, from_y: usize) -> usize {
+        let mut count = 0;
+
+        for x in 0..self.width {
+            for y in 0..self.height {
+                if self.get(x, y) && ((x != from_x) || (y != from_y)) {
+                    let diff_x = diff(x, from_x);
+                    let diff_y = diff(y, from_y);
+                    let gcd = gcd(diff_x, diff_y);
+                    let rise = diff_y / gcd;
+                    let run = diff_x / gcd;
+
+                    let mut curx = from_x;
+                    let mut cury = from_y;
+
+                    let shadowed = loop {
+                        let (newx, newy) = match (x > from_x, y > from_y) {
+                            // we're going down and right
+                            (true, true)  => (curx + run, cury + rise),
+                            // we're going up and right
+                            (true, false) => (curx + run, cury - rise),
+                            // we're going down and left
+                            (false, true) => (curx - run, cury + rise),
+                            // we're going up and left
+                            (false, false) => (curx - run, cury - rise),
+                        };
+
+                        if newx == x && newy == y {
+                            break false;
+                        }
+
+                        if self.get(newx, newy) {
+                            break true;
+                        }
+
+                        curx = newx;
+                        cury = newy;
+                    };
+
+                    if !shadowed {
+                        count += 1;
+                    }
+                }
+            }
+        }
+
+        count
+    }
+
+    fn place_station(&self) -> (usize, usize, usize) {
+        let mut most_found = 0;
+        let mut best_x = 0;
+        let mut best_y = 0;
+
+        for y in 0..self.height {
+            for x in 0..self.width {
+                if self.get(x, y) {
+                    let mine = self.count_visible(x, y);
+                    if mine > most_found {
+                        best_x = x;
+                        best_y = y;
+                        most_found = mine;
+                    }
+                }
+            }
+        }
+
+        (most_found, best_x, best_y)
+    }
+
+    fn print(&self) {
+        for y in 0..self.height {
+            for x in 0..self.width {
+                if self.get(x, y) {
+                    print!("#");
+                } else {
+                    print!(".");
+                }
+            }
+            println!();
+        }
+    }
+}
+
+fn diff(a: usize, b: usize) -> usize {
+    if a > b {
+        a - b
+    } else {
+        b - a
+    }
+}
+
+fn gcd(mut x: usize, mut y: usize) -> usize {
+    while y != 0 {
+        let t = x % y;
+        x = y;
+        y = t;
+    }
+    x
+}
+
+#[test]
+fn day10() {
+    let example1 = StationMap::new(".#..#\n.....\n#####\n....#\n...##\n");
+    assert_eq!((8, 3, 4), example1.place_station());
+    let example2 = StationMap::new("......#.#.\n#..#.#....\n..#######.\n.#.#.###..\n.#..#.....\n..#....#.#\n#..#....#.\n.##.#..###\n##...#..#.\n.#....####\n");
+    assert_eq!((33,5,8), example2.place_station());
+    let example3 = StationMap::new("#.#...#.#.\n.###....#.\n.#....#...\n##.#.#.#.#\n....#.#.#.\n.##..###.#\n..#...##..\n..##....##\n......#...\n.####.###.\n");
+    assert_eq!((35,1,2), example3.place_station());
+    let example4 = StationMap::new(".#..#..###\n####.###.#\n....###.#.\n..###.##.#\n##.##.#.#.\n....###..#\n..#.#..#.#\n#..#.#.###\n.##...##.#\n.....#.#..\n");
+    assert_eq!((41,6,3), example4.place_station());
+    let example5 = StationMap::new(".#..##.###...#######\n##.############..##.\n.#.######.########.#\n.###.#######.####.#.\n#####.##.#.##.###.##\n..#####..#.#########\n####################\n#.####....###.#.#.##\n##.#################\n#####.##.###..####..\n..######..##.#######\n####.##.####...##..#\n.#####..#.######.###\n##...#.##########...\n#.##########.#######\n.####.#.###.###.#.##\n....##.##.###..#####\n.#.#.###########.###\n#.#.#.#####.####.###\n###.##.####.##.#..##\n");
+    assert_eq!((210,11,13), example5.place_station());
+    let day10_contents = fs::read("inputs/day10").expect("Couldn't open day10 problem");
+    let day10_str = str::from_utf8(&day10_contents).expect("Couldn't decode day10 problem");
+    let day10a = StationMap::new(&day10_str);
+    day10a.print();
+    assert_eq!((334,23,20), day10a.place_station());
+}