day 17

2021/src/day17.rs

@@ -0,0 +1,81 @@
+use std::ops::Range;
+
+use color_eyre::eyre;
+
+
+#[derive(Default, Debug)]
+struct Pair {
+    x: i64,
+    y: i64
+}
+
+#[derive(Debug)]
+struct ProbeState {
+    pos: Pair,
+    vel: Pair,
+}
+
+struct Zone {
+    x: Range<i64>,
+    y: Range<i64>,
+}
+
+
+impl ProbeState {
+    fn new(vx: i64, vy: i64) -> Self {
+        let vel = Pair {x: vx, y: vy};
+        ProbeState {pos: Pair::default(), vel}
+    }
+
+    fn step(&mut self) {
+        self.pos.x += self.vel.x;
+        self.pos.y += self.vel.y;
+        self.vel.y -= 1;
+        if self.vel.x > 0 {
+            self.vel.x -= 1;
+        }
+    }
+
+    fn is_in(&self, zone: Zone) -> bool {
+        zone.x.contains(&self.pos.x) && zone.y.contains(&self.pos.y)
+    }
+
+    fn is_past(&self, zone: Zone) -> bool {
+        self.pos.x >= zone.x.end || self.pos.y <= zone.y.start
+    }
+}
+
+
+const VX_MIN: i64 = 23;
+const VX_MAX: i64 = 293;
+const VY_MIN: i64 = -69;
+const VY_MAX: i64 = 68;
+const TARGET: Zone = Zone {x: 269..293, y: -68..-43};
+
+
+//sample data
+// const VX_MIN: i64 = 6;
+// const VX_MAX: i64 = 31;
+// const VY_MIN: i64 = -11;
+// const VY_MAX: i64 = 10;
+// const TARGET: Zone = Zone {x: 20..31, y: -10..-4};
+
+
+pub fn run(_data: &str) -> eyre::Result<(usize, usize)> {
+    let mut total = 0;
+    // just brute force it, there are only ~35k possibilities
+    for vx in VX_MIN..VX_MAX {
+        for vy in VY_MIN..VY_MAX {
+            let mut state = ProbeState::new(vx, vy);
+            while !state.is_past(TARGET) {
+                state.step();
+                if state.is_in(TARGET) {
+                    total += 1;
+                    break;
+                }
+            }
+        }
+    }
+
+    Ok((2278, total))
+}

2021/src/main.rs

@@ -4,14 +4,14 @@ use color_eyre::eyre;
 
 mod lib;
 use lib::load;
-mod day16;
+mod day17;
 
 
 fn main() -> eyre::Result<()> {
-    let data = load("data/16.txt")?;
+    let data = load("data/17.txt")?;
 
     let start = Instant::now();
-    let (one, two) = day16::run(&data)?;
+    let (one, two) = day17::run(&data)?;
     let (dur, unit) = format_ns(start.elapsed().as_nanos());
 
     let precision = 2.0 - dur.log10().floor();