Solutions to day 13.

2016/day-13/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "day-13"
+version = "0.1.0"
+authors = ["Bert Peters <bert.ljpeters@gmail.com>"]
+
+[dependencies]

2016/day-13/src/main.rs

@@ -0,0 +1,57 @@
+use std::collections::HashSet;
+use std::collections::VecDeque;
+
+const INPUT: i64 = 1352;
+
+fn is_wall(x: i64, y: i64) -> bool
+{
+    if x < 0 || y < 0 {
+        return true;
+    }
+
+    let num = x*x + 3*x + 2*x*y + y + y*y + INPUT;
+
+    num.count_ones() % 2 == 1
+}
+
+fn main() {
+
+    let target = (31, 39);
+
+    let mut visited = HashSet::new();
+    visited.insert((1i64, 1i64));
+
+    let mut todo = VecDeque::new();
+    todo.push_back((0, 1i64, 1i64));
+
+    let mut count = 1;
+
+    while !todo.is_empty()
+    {
+        let (dist, x, y) = todo.pop_front().unwrap();
+
+        for i in -1..2 { // -1, 0, 1
+            for j in -1..2 {
+                let new_pos = (x + i, y + j);
+
+                if i.abs() == j.abs() || is_wall(x + i, y + j) || visited.contains(&new_pos) {
+                    continue;
+                }
+
+                if new_pos == target {
+                    println!("Reached pos {:?} at dist {}", new_pos, dist + 1);
+                    break;
+                }
+
+                todo.push_back((dist + 1, x + i, y + j));
+
+                visited.insert(new_pos);
+                if dist < 50 {
+                    count += 1;
+                }
+            }
+        }
+    }
+
+    println!("Visisted {} locations withing 50 steps", count);
+}