day 9 part 1

day9/src/main.rs

@@ -0,0 +1,63 @@
+use itertools::Itertools;
+use std::fs::File;
+use std::io::{prelude::*, BufReader};
+
+fn main() -> std::io::Result<()> {
+    //Read in file
+    let file = File::open("input")?;
+    let reader = BufReader::new(file);
+
+    let mut tail_pos: Vec<(i32, i32)> = vec![(0, 0)];
+    let mut head_pos: Vec<(i32, i32)> = vec![(0, 0)];
+
+    //read in input
+    reader.lines().for_each(|line| {
+        let line = line.unwrap();
+        let (direction, steps) = match line.split(' ').collect::<Vec<&str>>()[..] {
+            [dir, step] => (dir, step.parse::<usize>().unwrap()),
+            _ => panic!("failed parseing line {}", line),
+        };
+        for _ in 0..steps {
+            let (mut cur_head_x, mut cur_head_y) = head_pos.last().unwrap();
+            let (mut cur_tail_x, mut cur_tail_y) = tail_pos.last().unwrap();
+            match direction {
+                "L" => cur_head_x -= 1,
+                "R" => cur_head_x += 1,
+                "U" => cur_head_y += 1,
+                "D" => cur_head_y -= 1,
+                x => panic!("invalid movement {}", x),
+            };
+            let x_offset = cur_head_x - cur_tail_x;
+            let y_offset = cur_head_y - cur_tail_y;
+            if x_offset > 1 {
+                if y_offset != 0 {
+                    cur_tail_y = cur_head_y;
+                }
+                cur_tail_x += 1
+            } else if x_offset < -1 {
+                if y_offset != 0 {
+                    cur_tail_y = cur_head_y;
+                }
+                cur_tail_x -= 1
+            } else if y_offset > 1 {
+                if x_offset != 0 {
+                    cur_tail_x = cur_head_x;
+                }
+                cur_tail_y += 1
+            } else if y_offset < -1 {
+                if x_offset != 0 {
+                    cur_tail_x = cur_head_x;
+                }
+                cur_tail_y -= 1
+            }
+            let new_tail = (cur_tail_x, cur_tail_y);
+            if *tail_pos.last().unwrap() != new_tail {
+                tail_pos.push(new_tail);
+            }
+            head_pos.push((cur_head_x, cur_head_y));
+        }
+    });
+    let part1 = tail_pos.iter().unique().count();
+    println!("Part 1: {}", part1);
+    Ok(())
+}