From bf5747e9925988c8cf053f974fdcc35ca76df361 Mon Sep 17 00:00:00 2001
From: Gard Spreemann <gspr@nonempty.org>
Date: Sun, 11 Dec 2022 16:14:28 +0100
Subject: Days 8 and 9

---
 09/src/part-2.rs | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 09/src/part-2.rs

(limited to '09/src/part-2.rs')

diff --git a/09/src/part-2.rs b/09/src/part-2.rs
new file mode 100644
index 0000000..1773d2e
--- /dev/null
+++ b/09/src/part-2.rs
@@ -0,0 +1,65 @@
+// Ugh, weird motion in this grid world!
+
+use std::collections::{HashSet};
+use std::io::{BufRead};
+
+const NUM_SEGMENTS: usize = 10;
+
+type Pos = [isize; 2];
+
+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 positions: [Pos; NUM_SEGMENTS] = [[0; 2]; NUM_SEGMENTS];
+    seen.insert(positions[NUM_SEGMENTS-1].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' => positions[0][0] -= 1,
+                b'R' => positions[0][0] += 1,
+                b'U' => positions[0][1] += 1,
+                b'D' => positions[0][1] -= 1,
+                _    => panic!("Malformed input")
+            };
+
+            for i in 1..NUM_SEGMENTS {
+                let delta: [isize; 2] = {
+                    let mut ret: [isize; 2] = [0; 2];
+                    for d in 0..2 { ret[d] = positions[i-1][d] - positions[i][d]; }
+                    ret
+                };
+                if delta[0].abs() == 2 {
+                    positions[i][0] += delta[0].signum();
+                    if delta[1].abs() == 1 {
+                        positions[i][1] += delta[1].signum();
+                    }
+                }
+                if delta[1].abs() == 2 {
+                    positions[i][1] += delta[1].signum();
+                    if delta[0].abs() == 1 {
+                        positions[i][0] += delta[0].signum();
+                    }
+                }
+            }
+            seen.insert(positions[NUM_SEGMENTS-1].clone());
+        }
+    }
+
+    println!("{}", seen.len());
+
+    
+}
-- 
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