1 files changed, 59 insertions, 0 deletions
diff --git a/09/src/part-1.rs b/09/src/part-1.rs
new file mode 100644
index 0000000..f61c09d
--- /dev/null
+++ b/09/src/part-1.rs
@@ -0,0 +1,59 @@
+use std::collections::{HashSet};
+use std::io::{BufRead};
+
+
+fn main() {
+    let stdin = std::io::stdin();
+    let mut handle = stdin.lock();
+
+    let mut buf: Vec<u8> = Vec::new();
+    let mut seen: HashSet<[isize; 2]> = HashSet::new();
+    let mut head_pos: [isize; 2] = [0; 2];
+    let mut tail_pos: [isize; 2] = head_pos.clone();
+    seen.insert(tail_pos.clone());
+
+    loop {
+        buf.clear();
+        let num_bytes = handle.read_until(b'\n', &mut buf).expect("IO error");
+        if num_bytes == 0 { break; }
+
+        if buf[buf.len() - 1] == b'\n' { buf.pop(); }
+
+        let direction = buf[0];
+        let num_steps: usize = std::str::from_utf8(& buf[2..]).expect("Malformed input")
+            .parse().expect("Malformed input");
+
+        for dir in std::iter::repeat(direction).take(num_steps) {
+            match dir {
+                b'L' => head_pos[0] -= 1,
+                b'R' => head_pos[0] += 1,
+                b'U' => head_pos[1] += 1,
+                b'D' => head_pos[1] -= 1,
+                _    => panic!("Malformed input")
+            };
+            let delta: [isize; 2] = {
+                let mut ret: [isize; 2] = [0; 2];
+                for i in 0..2 { ret[i] = head_pos[i] - tail_pos[i]; }
+                ret
+            };
+            if delta[0].abs() == 2 {
+                tail_pos[0] += delta[0].signum();
+                if delta[1].abs() == 1 {
+                    tail_pos[1] += delta[1].signum();
+                }
+                seen.insert(tail_pos.clone());
+            }
+            else if delta[1].abs() == 2 {
+                tail_pos[1] += delta[1].signum();
+                if delta[0].abs() == 1 {
+                    tail_pos[0] += delta[0].signum();
+                }
+                seen.insert(tail_pos.clone());
+            }
+        }
+    }
+
+    println!("{}", seen.len());
+
+    
+}