From 56fb300d3b93cdcec45001a8563119234cd1fe80 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Sat, 16 Dec 2017 22:19:05 +0100
Subject: [PATCH] Implement day 14 in rust.

---
 2017/day-14/solution.rs | 126 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 126 insertions(+)
 create mode 100644 2017/day-14/solution.rs

diff --git a/2017/day-14/solution.rs b/2017/day-14/solution.rs
new file mode 100644
index 0000000..9293f47
--- /dev/null
+++ b/2017/day-14/solution.rs
@@ -0,0 +1,126 @@
+use std::io;
+use std::collections::VecDeque;
+
+fn hash(input: &str, output: &mut[u8])
+{
+    let mut buffer = [0u8; 256];
+    for i in {0..256} {
+        buffer[i] = i as u8;
+    }
+
+    let mut actual_key = String::from(input);
+    // Needed to convert to hex
+    actual_key += "\x11\x1f\x49\x2f\x17";
+
+    let mut index = 0u8;
+    let mut skip = 0u8;
+
+    for _ in 0..64 {
+        for c in actual_key.chars() {
+            let offset = c as u8;
+
+            for i in 0..(offset / 2) {
+                let i1 = index.wrapping_add(i) as usize;
+                let i2 = index.wrapping_add(offset).wrapping_sub(i).wrapping_sub(1) as usize;
+
+                let temp = buffer[i1];
+                buffer[i1] = buffer[i2];
+                buffer[i2] = temp;
+            }
+
+            index = index.wrapping_add(offset).wrapping_add(skip);
+            skip = skip.wrapping_add(1);
+        }
+    }
+
+    for (i, b) in buffer.iter().enumerate() {
+        output[i / 16] ^= b;
+    }
+}
+
+fn count_ones(input: &[[u8; 16]]) -> u32
+{
+    let mut total: u32 = 0;
+    for row in input {
+        let row_total: u32 = row.iter().map(|x| x.count_ones()).sum();
+        total += row_total;
+    }
+
+    return total;
+}
+
+fn get_hash(input: &str) -> [[u8; 16]; 128]
+{
+    let mut hash_buffer = [[0u8; 16]; 128];
+
+    for i in 0..128 {
+        let mut hash_key = String::from(input);
+        hash_key += "-";
+        hash_key += &i.to_string();
+
+        hash(&hash_key, &mut hash_buffer[i]);
+    }
+
+    return hash_buffer;
+}
+
+fn is_used(hashes: &[[u8; 16]], y: usize, x: usize) -> bool
+{
+    let byte = hashes[y][x / 8];
+
+    return (byte & (1 << (7 - (x % 8)))) != 0;
+}
+
+fn count_groups(hashes: &[[u8; 16]]) -> u32
+{
+    let mut visited = [[false; 128]; 128];
+
+    let mut groups = 0u32;
+
+    for x in 0..128 {
+        for y in 0..128 {
+            if visited[x][y] || !is_used(hashes, x, y) {
+                continue;
+            }
+            visited[x][y] = true;
+            groups += 1;
+
+            let mut todo = VecDeque::new();
+            todo.push_back((x, y));
+
+            while !todo.is_empty() {
+                let (cur_x, cur_y) = todo.pop_front().unwrap();
+
+                let x_min = if cur_x == 0 { 0 } else { cur_x - 1 };
+                let y_min = if cur_y == 0 { 0 } else { cur_y - 1 };
+                let x_max = if cur_x == 127 { 128 } else { cur_x + 2 };
+                let y_max = if cur_y == 127 { 128 } else { cur_y + 2 };
+
+                for x_new in x_min..(x_max) {
+                    for y_new in y_min..(y_max) {
+                        if (cur_x != x_new) ^ (cur_y != y_new) && !visited[x_new][y_new] && is_used(hashes, x_new, y_new) {
+                            visited[x_new][y_new] = true;
+                            todo.push_back((x_new, y_new));
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    return groups;
+}
+
+
+fn main()
+{
+    let reader = io::stdin();
+
+    let mut input = String::new();
+    reader.read_line(&mut input).unwrap();
+
+    let hashes = get_hash(input.trim());
+
+    println!("Part 1: {}", count_ones(&hashes));
+    println!("Part 2: {}", count_groups(&hashes));
+}