2015 day 3

2015/src/bin/day3.rs

@@ -0,0 +1,45 @@
+use std::collections::HashMap;
+
+use aoc::input;
+
+fn main() {
+    let chars = input::read_chars();
+
+    // Part 1
+    let mut houses = HashMap::<(i32, i32), u32>::new();
+    let (mut x, mut y) = (0, 0);
+    houses.insert((0, 0), 1);
+    for c in chars.chars() {
+        match c {
+            '>' => x += 1,
+            '<' => x -= 1,
+            'v' => y += 1,
+            '^' => y -= 1,
+            _ => {}
+        }
+        let presents = houses.entry((x, y)).or_insert(0);
+        *presents += 1;
+    }
+    let num_houses = houses.values().filter(|v| **v > 0).count();
+    println!("Houses delivered: {}.", num_houses);
+
+    // Part 2
+    let mut houses = HashMap::<(i32, i32), u32>::new();
+    let (mut x, mut y, mut rx, mut ry) = (0, 0, 0, 0);
+    houses.insert((0, 0), 1);
+    let mut is_robot_turn = false;
+    for c in chars.chars() {
+        match c {
+            '>' => if is_robot_turn { rx += 1 } else { x += 1 },
+            '<' => if is_robot_turn { rx -= 1 } else { x -= 1 },
+            'v' => if is_robot_turn { ry += 1 } else { y += 1 },
+            '^' => if is_robot_turn { ry -= 1 } else { y -= 1 },
+            _ => {}
+        }
+        let presents = houses.entry(if is_robot_turn { (rx, ry) } else { (x, y) }).or_insert(0);
+        *presents += 1;
+        is_robot_turn = !is_robot_turn;
+    }
+    let num_houses = houses.values().filter(|v| **v > 0).count();
+    println!("Houses delivered: {}.", num_houses);
+}

2015/src/input.rs

@@ -15,3 +15,7 @@ pub fn read_lines() -> Vec<String> {
     }
     lines
 }
+
+pub fn read_chars() -> String {
+    read_lines()[0].to_owned()
+}