From ad781231e956297015169ad392942b7141ff3e1e Mon Sep 17 00:00:00 2001
From: Julius de Jeu <julius@voidcorp.nl>
Date: Fri, 17 Dec 2021 10:08:53 +0100
Subject: [PATCH] Day 17

---
 input/day17  |   1 +
 src/day17.rs | 105 +++++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.rs  |   5 ++-
 3 files changed, 110 insertions(+), 1 deletion(-)
 create mode 100644 input/day17
 create mode 100644 src/day17.rs

diff --git a/input/day17 b/input/day17
new file mode 100644
index 0000000..84da003
--- /dev/null
+++ b/input/day17
@@ -0,0 +1 @@
+target area: x=277..318, y=-92..-53
\ No newline at end of file
diff --git a/src/day17.rs b/src/day17.rs
new file mode 100644
index 0000000..cefedfe
--- /dev/null
+++ b/src/day17.rs
@@ -0,0 +1,105 @@
+use std::cmp::Ordering;
+use crate::Day;
+
+pub struct Day17 {
+    x_min: i32,
+    x_max: i32,
+    y_min: i32,
+    y_max: i32,
+}
+
+impl Day for Day17 {
+    fn init(content: String) -> anyhow::Result<Self> {
+        let c = content.split(' ').skip(1).collect::<Vec<_>>();
+        let (x_min, x_max) = c[1][2..(c[1].len() - 1)].split_once("..").unwrap();
+        let (y_min, y_max) = c[2][2..].split_once("..").unwrap();
+
+        Ok(Day17 {
+            x_min: x_min.parse()?,
+            x_max: x_max.parse()?,
+            y_min: y_min.parse()?,
+            y_max: y_max.parse()?,
+        })
+    }
+
+    fn part1(&self) -> anyhow::Result<String> {
+        let mut hits = Vec::new();
+        for dx in 0..=self.x_max {
+            for dy in -100..250 {
+                let points = self.calc((dx, dy));
+                if self.hits(&points) {
+                    hits.push(max_height(&points).unwrap());
+                }
+            }
+        }
+        Ok(format!("{}", hits.iter().max().unwrap()))
+    }
+
+    fn part2(&self) -> anyhow::Result<String> {
+        let mut hits = Vec::new();
+        for dx in 0..=self.x_max {
+            for dy in -100..250 {
+                let points = self.calc((dx, dy));
+                if self.hits(&points) {
+                    hits.push((dx, dy));
+                }
+            }
+        }
+        Ok(format!("{}", hits.len()))
+    }
+}
+
+impl Day17 {
+    fn hits(&self, points: &[(i32, i32)]) -> bool {
+        points.iter().any(|&(x, y)| x >= self.x_min && x <= self.x_max && y >= self.y_min && y <= self.y_max)
+    }
+
+    fn calc(&self, initial_velocity: (i32, i32)) -> Vec<(i32, i32)> {
+        let mut steps = vec![(0, 0)];
+        let mut velocity = initial_velocity;
+
+        loop {
+            let (x, y) = steps.last().unwrap();
+            let (x, y) = (x + velocity.0, y + velocity.1);
+            if x > self.x_max || y < self.y_min {
+                break;
+            }
+            steps.push((x, y));
+            match velocity.0.cmp(&0) {
+                Ordering::Less => velocity.0 += 1,
+                Ordering::Equal => {}
+                Ordering::Greater => velocity.0 -= 1,
+            }
+            velocity.1 -= 1;
+        }
+        steps
+    }
+}
+
+fn max_height(points: &[(i32, i32)]) -> Option<i32> {
+    points.iter().map(|&x| x.1).max()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{Day, day_tests};
+    use crate::day17::Day17;
+
+    const INPUT: &str = "target area: x=20..30, y=-10..-5";
+
+    #[test]
+    fn part1_test() -> anyhow::Result<()> {
+        let d = Day17::init(INPUT.to_string())?;
+        assert_eq!("45", d.part1()?);
+        Ok(())
+    }
+
+    #[test]
+    fn part2_test() -> anyhow::Result<()> {
+        let d = Day17::init(INPUT.to_string())?;
+        assert_eq!("112", d.part2()?);
+        Ok(())
+    }
+
+    day_tests!(Day17, "17", "4186", "2709");
+}
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index 6f4245d..d29992b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -19,6 +19,7 @@ use crate::day13::Day13;
 use crate::day14::Day14;
 use crate::day15::Day15;
 use crate::day16::Day16;
+use crate::day17::Day17;
 
 mod day;
 mod day01;
@@ -37,6 +38,7 @@ mod day13;
 mod day14;
 mod day15;
 mod day16;
+mod day17;
 
 fn load_input(day: &str) -> Result<String> {
     read_to_string(format!("./input/day{}", day)).map_err(|x| x.into())
@@ -87,7 +89,8 @@ fn main() -> anyhow::Result<()> {
                                        Box::new(Day13::init(load_input("13")?)?),
                                        Box::new(Day14::init(load_input("14")?)?),
                                        Box::new(Day15::init(load_input("15")?)?),
-                                       Box::new(Day16::init(load_input("16")?)?),];
+                                       Box::new(Day16::init(load_input("16")?)?),
+                                       Box::new(Day17::init(load_input("17")?)?),];
 
     let _verbosity = matches.occurrences_of("v");
     if matches.is_present("all") {