Day 17

input/17-test.txt

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+target area: x=20..30, y=-10..-5

input/17.txt

@@ -0,0 +1 @@
+target area: x=88..125, y=-157..-103

src/bin/17.rs

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+fn main() {
+    let (max_y, count) = solve();
+    println!("First solution: {:?}", max_y);
+    println!("Second solution: {:?}", count);
+}
+
+fn solve() -> (i32, i32) {
+    let mut max_y = 0;
+    let mut count = 0;
+
+    for vx in 1..150 {
+        for vy in -1000..1000 {
+            if let Some(y) = check_trajectory(vx, vy) {
+                count += 1;
+                max_y = max_y.max(y);
+            }
+        }
+    }
+
+    (max_y, count)
+}
+
+/// Returns the largest y if it hits the target.
+fn check_trajectory(mut vx: i32, mut vy: i32) -> Option<i32> {
+    let mut pos = Position::default();
+    let mut max_y = 0;
+    let target = input();
+
+    loop {
+        pos.x += vx;
+        pos.y += vy;
+        vx -= vx.signum();
+        vy -= 1;
+        max_y = max_y.max(pos.y);
+
+        if target.contains(pos) {
+            return Some(max_y);
+        }
+        if pos.y < target.min.y {
+            // We are below the target
+            return None;
+        }
+        if pos.x > target.max.x {
+            // We are too far right
+            return None;
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+struct Position {
+    x: i32,
+    y: i32,
+}
+
+#[derive(Debug)]
+struct Target {
+    min: Position,
+    max: Position,
+}
+
+impl Target {
+    fn contains(&self, p: Position) -> bool {
+        p.x >= self.min.x && p.x <= self.max.x && p.y >= self.min.y && p.y <= self.max.y
+    }
+}
+
+fn input() -> Target {
+    let file = include_str!("../../input/17.txt");
+    let (_, coords) = file.split_once(": ").unwrap();
+    let (x, y) = coords.split_once(", ").unwrap();
+    let x = &x[2..];
+    let y = &y[2..];
+
+    let (x_min, x_max) = x.split_once("..").unwrap();
+    let (y_min, y_max) = y.split_once("..").unwrap();
+
+    Target {
+        min: Position {
+            x: x_min.parse().unwrap(),
+            y: y_min.parse().unwrap(),
+        },
+        max: Position {
+            x: x_max.parse().unwrap(),
+            y: y_max.parse().unwrap(),
+        },
+    }
+}