Add solutions for day 17.

2016/day-17/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "day-17"
+version = "0.1.0"
+authors = ["Bert Peters <bert.ljpeters@gmail.com>"]
+
+[dependencies]
+rust-crypto = "0.2.36"

2016/day-17/src/main.rs

@@ -0,0 +1,74 @@
+extern crate crypto;
+
+use crypto::md5::Md5;
+use crypto::digest::Digest;
+use std::collections::VecDeque;
+
+const INPUT: &'static str = "pxxbnzuo";
+
+const DIRECTIONS: [char; 4] = [
+    'U',
+    'D',
+    'L',
+    'R',
+];
+
+const DELTAS: [(i32, i32); 4] = [
+    (0, -1),
+    (0, 1),
+    (-1, 0),
+    (1, 0),
+];
+
+fn open_doors(route: &str) -> [bool; 4]
+{
+    let mut hasher = Md5::new();
+    hasher.input_str(INPUT);
+    hasher.input_str(route);
+
+    let mut output = [0u8; 16];
+    hasher.result(&mut output);
+
+    return [
+        (output[0] >> 4) > 0xa,
+        (output[0] & 0xf) > 0xa,
+        (output[1] >> 4) > 0xa,
+        (output[1] & 0xf) > 0xa,
+    ];
+}
+
+fn main() {
+    let mut todo = VecDeque::new();
+    todo.push_back(((0i32, 0i32), String::new()));
+
+    let mut last = String::new();
+
+    while !todo.is_empty() {
+        let ((x, y), path) = todo.pop_front().unwrap();
+        if x == 3 && y == 3 {
+            if &last == "" {
+                println!("Found route out! {}", path);
+            }
+
+            last = path;
+
+            continue;
+        }
+
+        let doors = open_doors(&path);
+
+        for (index, &(x_d, y_d)) in DELTAS.iter().enumerate() {
+            if !doors[index] || x + x_d < 0 || x + x_d >= 4 || y + y_d < 0 || y + y_d >= 4 {
+                continue;
+            }
+
+            let new_pos = (x + x_d, y + y_d);
+            let mut new_path = path.clone();
+            new_path.push(DIRECTIONS[index]);
+
+            todo.push_back((new_pos, new_path));
+        }
+    }
+
+    println!("Longest path length: {}", last.len());
+}