1 files changed, 91 insertions, 0 deletions
diff --git a/2022/src/bin/day_20.rs b/2022/src/bin/day_20.rs
new file mode 100644
index 0000000..dc4bf4f
--- /dev/null
+++ b/2022/src/bin/day_20.rs
@@ -0,0 +1,91 @@
+use nom::{
+    character::complete::{i64, line_ending},
+    combinator::map,
+    multi::separated_list1,
+    IResult,
+};
+use std::fs;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("inputs/day_20.txt")?;
+    let coordinates = GroveCoordinates::parser(&input).unwrap().1;
+
+    {
+        let mut coordinates_1 = coordinates.clone();
+        coordinates_1.mix();
+        dbg!(coordinates_1.coordinate_sum());
+    }
+
+    {
+        let mut coordinates_2 = coordinates.clone();
+        coordinates_2.decrypt(811589153);
+        dbg!(coordinates_2.coordinate_sum());
+    }
+
+    Ok(())
+}
+
+#[derive(Debug, Clone)]
+struct GroveCoordinates(Vec<CoordinatePoint>);
+
+#[derive(Debug, Clone, Copy)]
+struct CoordinatePoint {
+    val: i64,
+    original_order: usize,
+}
+
+impl GroveCoordinates {
+    fn parser(input: &str) -> IResult<&str, Self> {
+        map(separated_list1(line_ending, i64), |points| {
+            GroveCoordinates(
+                points
+                    .into_iter()
+                    .enumerate()
+                    .map(|(original_order, val)| CoordinatePoint {
+                        val,
+                        original_order,
+                    })
+                    .collect(),
+            )
+        })(input)
+    }
+
+    fn decrypt(&mut self, key: i64) {
+        for p in &mut self.0 {
+            p.val *= key;
+        }
+
+        for _ in 0..10 {
+            self.mix();
+        }
+    }
+
+    fn mix(&mut self) {
+        for original_i in 0..self.0.len() {
+            let encrypted_i = self
+                .0
+                .iter()
+                .position(|p| p.original_order == original_i)
+                .unwrap();
+            let to_move = self.0.remove(encrypted_i);
+
+            let mut destination_i = encrypted_i as i64 + to_move.val;
+            destination_i %= self.0.len() as i64;
+            if destination_i < 0 {
+                destination_i += self.0.len() as i64;
+            }
+            self.0.insert(destination_i as usize, to_move);
+        }
+    }
+
+    fn get(&self, i: usize) -> i64 {
+        self.0[i % self.0.len()].val
+    }
+
+    fn coordinate_sum(&self) -> i64 {
+        let zero_position = self.0.iter().position(|p| p.val == 0).unwrap();
+        self.get(zero_position + 1000)
+            + self.get(zero_position + 2000)
+            + self.get(zero_position + 3000)
+    }
+}