1 files changed, 219 insertions, 0 deletions
diff --git a/16/src/main.rs b/16/src/main.rs
new file mode 100644
index 0000000..f4f6253
--- /dev/null
+++ b/16/src/main.rs
@@ -0,0 +1,219 @@
+use advent_lib::prelude::*;
+
+#[derive(Debug)]
+struct Packet {
+  version: u8,
+  type_id: u8,
+  content: Vec<u8>,
+  subpackets: Vec<Packet>,
+}
+
+
+fn main() -> Result<()> {
+  let mut args = std::env::args();
+  if args.len() != 2 {
+    eprintln!("Usage: advent input");
+  }
+  let _ = args.next();
+  let filename = args.next().unwrap();
+
+  let input = advent_lib::read_lines_file(&filename)?;
+
+  let mut bit_string: Vec<u8> = Vec::new();
+  for c in input[0].chars() {
+    let value = c.to_digit(16).unwrap() as u8;
+    for i in 0 .. 4 {
+      let bit = (value >> (3 - i)) & 1;
+      bit_string.push(bit);
+    }
+  }
+
+  let mut iter = bit_string.iter().peekable();
+  let (version_total, _top_packet, result) = read_packet(&mut iter).unwrap();
+  println!("{}", version_total);
+  println!("{}", result);
+
+  Ok(())
+}
+
+
+fn read_packet<'a>(iter: &mut impl Iterator<Item=&'a u8>) -> Result<(u64, Packet, u128)>
+{
+  let mut version_total: u64 = 0;
+
+  let version = bits_to_u8(take_bits(iter, 3)?);
+  let type_id = bits_to_u8(take_bits(iter, 3)?);
+
+  version_total += version as u64;
+
+  if type_id == 4 {
+    let mut result = 0;
+    loop {
+      let bits = take_bits(iter, 5)?;
+
+      let bits_value = bits_to_u128(bits[1..].to_vec());
+      result = result << 4;
+      result += bits_value;
+
+      if bits[0] == 0 {
+        break;
+      }
+    }
+
+    Ok((version_total, Packet {
+      version,
+      type_id,
+      content: Vec::new(),
+      subpackets: Vec::new(),
+    }, result))
+  } else {
+    let mut subpackets = Vec::new();
+    let mut parameters = Vec::new();
+
+    let length_type_id = bits_to_u8(take_bits(iter, 1)?);
+    if length_type_id == 0 {
+      let length_in_bits = bits_to_u64(take_bits(iter, 15)?);
+
+      let mut content_bits: Vec<u8> = Vec::new();
+      for bit in iter.take(length_in_bits as usize) {
+        content_bits.push(*bit);
+      }
+
+      let mut content_bits = content_bits.iter().peekable();
+
+      loop {
+        match read_packet(&mut content_bits) {
+          Err(_) => {
+            break;
+          }
+          Ok((sub_version_total, subpacket, value)) => {
+            version_total += sub_version_total;
+            subpackets.push(subpacket);
+            parameters.push(value);
+          }
+        }
+      }
+    } else {
+      let n_subpackets = bits_to_u64(take_bits(iter, 11)?);
+
+      for _ in 0 .. n_subpackets {
+        match read_packet(iter) {
+          Err(_) => {
+            return Err(advent_lib::error::Error::Unspecified);
+          }
+          Ok((sub_version_total, subpacket, value)) => {
+            version_total += sub_version_total;
+            subpackets.push(subpacket);
+            parameters.push(value);
+          }
+        }
+      }
+    }
+
+    let mut result = 0;
+    match type_id {
+      0 => {
+        result = 0;
+        for parameter in &parameters {
+          result += parameter;
+        }
+      }
+      1 => {
+        result = 1;
+        for parameter in &parameters {
+          result *= parameter;
+        }
+      }
+      2 => {
+        result = parameters[0];
+        for parameter in &parameters {
+          if *parameter < result {
+            result = *parameter;
+          }
+        }
+      }
+      3 => {
+        result = parameters[0];
+        for parameter in &parameters {
+          if *parameter > result {
+            result = *parameter;
+          }
+        }
+      }
+      5 => {
+        result = if parameters[0] > parameters[1] { 1 } else { 0 };
+      }
+      6 => {
+        result = if parameters[0] < parameters[1] { 1 } else { 0 };
+      }
+      7 => {
+        result = if parameters[0] == parameters[1] { 1 } else { 0 };
+      }
+      _ => { }
+    }
+
+    Ok((version_total, Packet {
+      version,
+      type_id,
+      content: Vec::new(),
+      subpackets: subpackets,
+    }, result))
+  }
+}
+
+
+fn take_bits<'a>(iter: &mut impl Iterator<Item=&'a u8>, count: usize)
+  -> Result<Vec<u8>>
+{
+  let mut result: Vec<u8> = Vec::new();
+
+  for _ in 0 .. count {
+    match iter.next() {
+      None => {
+        return Err(advent_lib::error::Error::Unspecified);
+      }
+      Some(bit) => {
+        result.push(*bit);
+      }
+    }
+  }
+
+  Ok(result)
+}
+
+
+fn bits_to_u8(bits: Vec<u8>) -> u8 {
+  let mut result = 0;
+
+  for bit in &bits {
+    result *= 2;
+    result += bit;
+  }
+
+  result
+}
+
+
+fn bits_to_u64(bits: Vec<u8>) -> u64 {
+  let mut result = 0;
+
+  for bit in &bits {
+    result *= 2;
+    result += *bit as u64;
+  }
+
+  result
+}
+
+
+fn bits_to_u128(bits: Vec<u8>) -> u128 {
+  let mut result = 0;
+
+  for bit in &bits {
+    result *= 2;
+    result += *bit as u128;
+  }
+
+  result
+}
+