d9p2

day9/src/main.rs

@@ -6,34 +6,44 @@ use std::collections::HashSet;
 fn main() {
     let file = File::open(&env::args().nth(1).unwrap()).unwrap();
     let reader = io::BufReader::new(file);
-    let (mut hx, mut hy, mut tx, mut ty) = (0, 0, 0, 0);
+    let mut rope: [(i64, i64); 10] = [(0, 0); 10];
     let mut visited: HashSet<(i64, i64)> = vec![(0, 0)].into_iter().collect();
 
     for line in reader.lines().flatten() {
-        let (movx, movy) = match line.chars().nth(0) {
-            Some('L') => (-1, 0),
-            Some('R') => (1, 0),
-            Some('U') => (0, -1),
-            Some('D') => (0, 1),
-            _ => (999, 999),
-        };
-        let count = line[2..].parse::<i64>().unwrap();
+        let ((movx, movy), count) = parse_line(line).unwrap();
         for _ in 0..count {
-            (hx, hy) = (hx + movx, hy + movy);
-            (tx, ty) = move_tail(hx, hy, tx, ty).unwrap();
-            visited.insert((tx, ty));
+            rope[0] = (rope[0].0 + movx, rope[0].1 + movy);
+            for link in 1..=9 {
+                rope[link] = move_tail(rope[link - 1], rope[link]);
+            }
+            visited.insert(rope[9]);
         }
     }
     println!("{:?}", visited.len());
 }
 
-fn move_tail(hx: i64, hy: i64, tx: i64, ty: i64) -> Option<(i64, i64)> {
-    match (hx - tx, hy - ty) {
-        (-1..=1, -1..=1) => Some((tx, ty)),
-        (-1..=1, 2) => Some((hx, ty + 1)),
-        (-1..=1, -2) => Some((hx, ty - 1)),
-        (2, -1..=1) => Some((tx + 1, hy)),
-        (-2, -1..=1) => Some((tx - 1, hy)),
-        _ => None
+fn parse_line(line: String) -> Option<((i64, i64), i64)> {
+    let mov = match line.chars().nth(0) {
+        Some('L') => Some((-1, 0)),
+        Some('R') => Some((1, 0)),
+        Some('U') => Some((0, -1)),
+        Some('D') => Some((0, 1)),
+        _ => None,
+    };
+    let count = line[2..].parse::<i64>();
+    match (mov, count) {
+        (Some(mov), Ok(count)) => Some((mov, count)),
+        _ => None,
+    }
+}
+
+fn move_tail((hx, hy): (i64, i64), (tx, ty): (i64, i64)) -> (i64, i64) {
+    let dx = if hx > tx { 1 } else { -1 };
+    let dy = if hy > ty { 1 } else { -1 };
+    match (hx - tx, hy - ty) {
+        (-1..=1, -1..=1) => (tx, ty),
+        (-1..=1, _) => (hx, ty + dy),
+        (_, -1..=1) => (tx + dx, hy),
+        (_, _) => (tx + dx, ty + dy),
     }
 }

day9/src/main1.rs

@@ -0,0 +1,39 @@
+use std::env;
+use std::fs::File;
+use std::io::{self, BufRead};
+use std::collections::HashSet;
+
+fn main() {
+    let file = File::open(&env::args().nth(1).unwrap()).unwrap();
+    let reader = io::BufReader::new(file);
+    let (mut hx, mut hy, mut tx, mut ty) = (0, 0, 0, 0);
+    let mut visited: HashSet<(i64, i64)> = vec![(0, 0)].into_iter().collect();
+
+    for line in reader.lines().flatten() {
+        let (movx, movy) = match line.chars().nth(0) {
+            Some('L') => (-1, 0),
+            Some('R') => (1, 0),
+            Some('U') => (0, -1),
+            Some('D') => (0, 1),
+            _ => (999, 999),
+        };
+        let count = line[2..].parse::<i64>().unwrap();
+        for _ in 0..count {
+            (hx, hy) = (hx + movx, hy + movy);
+            (tx, ty) = move_tail(hx, hy, tx, ty).unwrap();
+            visited.insert((tx, ty));
+        }
+    }
+    println!("{:?}", visited.len());
+}
+
+fn move_tail(hx: i64, hy: i64, tx: i64, ty: i64) -> Option<(i64, i64)> {
+    match (hx - tx, hy - ty) {
+        (-1..=1, -1..=1) => Some((tx, ty)),
+        (-1..=1, 2) => Some((hx, ty + 1)),
+        (-1..=1, -2) => Some((hx, ty - 1)),
+        (2, -1..=1) => Some((tx + 1, hy)),
+        (-2, -1..=1) => Some((tx - 1, hy)),
+        _ => None
+    }
+}

day9/test2.txt

@@ -0,0 +1,8 @@
+R 5
+U 8
+L 8
+D 3
+R 17
+D 10
+L 25
+U 20