diff --git a/Cargo.toml b/Cargo.toml
index 4851ca0..9bf8bc5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -62,3 +62,7 @@ path = "src/day14.rs"
 [[bin]]
 name = "day15"
 path = "src/day15.rs"
+
+[[bin]]
+name = "day16"
+path = "src/day16.rs"
diff --git a/inputs/day16.txt b/inputs/day16.txt
new file mode 100644
index 0000000..d1fbe79
--- /dev/null
+++ b/inputs/day16.txt
@@ -0,0 +1 @@
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
diff --git a/src/day16.rs b/src/day16.rs
new file mode 100644
index 0000000..afbfe06
--- /dev/null
+++ b/src/day16.rs
@@ -0,0 +1,283 @@
+use std::num::ParseIntError;
+use std::str::FromStr;
+
+#[derive(PartialEq, Clone, Debug)]
+enum PacketPayload {
+    Literal(u64),
+    Operator(u32, Vec<Packet>),
+}
+
+#[derive(Clone, Debug)]
+struct Packet {
+    version: u32,
+    payload: PacketPayload,
+}
+
+impl PartialEq for Packet {
+    fn eq(&self, other: &Self) -> bool {
+        self.version == other.version && self.payload == other.payload
+    }
+}
+
+type ParsePacketResult = Result<Packet, ParseIntError>;
+
+struct PacketParser<'a> {
+    s: std::str::Chars<'a>,
+}
+
+impl PacketParser<'_> {
+    fn new(s: &str) -> PacketParser {
+        PacketParser { s: s.chars() }
+    }
+
+    fn take_string(&mut self, n: usize) -> String {
+        (&mut self.s).take(n).collect()
+    }
+
+    fn parse_number(&mut self, bits: usize) -> Result<u32, ParseIntError> {
+        u32::from_str_radix(&self.take_string(bits), 2)
+    }
+
+    fn parse_operator(&mut self, id: u32) -> PacketPayload {
+        let mut packets;
+        match self.parse_number(1).unwrap() {
+            0 => {
+                let len = self.parse_number(15).unwrap() as usize;
+                let substring = self.take_string(len);
+                let sub_parser = &mut PacketParser::new(&substring);
+                packets = Vec::new();
+                while let Ok(packet) = sub_parser.parse_packet() {
+                    packets.push(packet);
+                }
+            }
+            1 => {
+                let n = self.parse_number(11).unwrap();
+                packets = Vec::with_capacity(n as usize);
+                for _ in 0..n {
+                    packets.push(self.parse_packet().unwrap());
+                }
+            }
+            _ => unreachable!(),
+        }
+        PacketPayload::Operator(id, packets)
+    }
+
+    fn parse_literal(&mut self) -> PacketPayload {
+        let mut n = 0_u64;
+        loop {
+            let first_bit = self.s.next().unwrap();
+            n = (n << 1) + self.s.next().unwrap().to_digit(2).unwrap() as u64;
+            n = (n << 1) + self.s.next().unwrap().to_digit(2).unwrap() as u64;
+            n = (n << 1) + self.s.next().unwrap().to_digit(2).unwrap() as u64;
+            n = (n << 1) + self.s.next().unwrap().to_digit(2).unwrap() as u64;
+            if first_bit == '0' {
+                break;
+            }
+        }
+        PacketPayload::Literal(n)
+    }
+
+    fn parse_packet(&mut self) -> ParsePacketResult {
+        let version = self.parse_number(3)?;
+        let payload = match self.parse_number(3)? {
+            4 => self.parse_literal(),
+            id => self.parse_operator(id),
+        };
+        Ok(Packet { version, payload })
+    }
+}
+
+impl FromStr for Packet {
+    type Err = ParseIntError;
+
+    fn from_str(s: &str) -> ParsePacketResult {
+        let s = s
+            .chars()
+            .map(|c| c.to_digit(16).unwrap())
+            .map(|n| format!("{:04b}", n))
+            .collect::<String>();
+        let mut parser = PacketParser::new(&s);
+        parser.parse_packet()
+    }
+}
+
+fn sum_version_numbers(p: &Packet) -> u32 {
+    match &p.payload {
+        PacketPayload::Literal(_) => p.version as u32,
+        PacketPayload::Operator(_, subpackets) => {
+            p.version + subpackets.iter().map(sum_version_numbers).sum::<u32>()
+        }
+    }
+}
+
+fn eval_packet(p: &Packet) -> u64 {
+    match &p.payload {
+        PacketPayload::Literal(n) => *n as u64,
+        PacketPayload::Operator(id, subpackets) => match id {
+            0 => subpackets.iter().map(eval_packet).sum::<u64>(),
+            1 => subpackets.iter().map(eval_packet).product::<u64>(),
+            2 => subpackets.iter().map(eval_packet).min().unwrap(),
+            3 => subpackets.iter().map(eval_packet).max().unwrap(),
+            5 => {
+                assert_eq!(subpackets.len(), 2);
+                if eval_packet(&subpackets[0]) > eval_packet(&subpackets[1]) {
+                    1
+                } else {
+                    0
+                }
+            }
+            6 => {
+                assert_eq!(subpackets.len(), 2);
+                if eval_packet(&subpackets[0]) < eval_packet(&subpackets[1]) {
+                    1
+                } else {
+                    0
+                }
+            }
+            7 => {
+                assert_eq!(subpackets.len(), 2);
+                if eval_packet(&subpackets[0]) == eval_packet(&subpackets[1]) {
+                    1
+                } else {
+                    0
+                }
+            }
+            _ => panic!("invalid operator ID {}", id),
+        },
+    }
+}
+
+fn main() -> Result<(), ParseIntError> {
+    let input = include_str!("../inputs/day16.txt").trim_end();
+    let packet: Packet = input.parse()?;
+    println!("solution {}", sum_version_numbers(&packet));
+    println!("solution {}", eval_packet(&packet));
+    Ok(())
+}
+
+#[test]
+fn test_literal() {
+    let packet: Packet = "D2FE28".parse().unwrap();
+    assert_eq!(
+        packet,
+        Packet {
+            version: 6,
+            payload: PacketPayload::Literal(2021)
+        }
+    );
+}
+
+#[test]
+fn test_parse_type_0_operator() {
+    let packet: Packet = "38006F45291200".parse().unwrap();
+    let packets = vec![
+        Packet {
+            version: 6,
+            payload: PacketPayload::Literal(10),
+        },
+        Packet {
+            version: 2,
+            payload: PacketPayload::Literal(20),
+        },
+    ];
+    assert_eq!(
+        packet,
+        Packet {
+            version: 1,
+            payload: PacketPayload::Operator(6, packets)
+        }
+    );
+}
+
+#[test]
+fn test_parse_type_1_operator() {
+    let packet: Packet = "EE00D40C823060".parse().unwrap();
+    assert_eq!(
+        packet,
+        Packet {
+            version: 7,
+            payload: PacketPayload::Operator(
+                3,
+                vec![
+                    Packet {
+                        version: 2,
+                        payload: PacketPayload::Literal(1)
+                    },
+                    Packet {
+                        version: 4,
+                        payload: PacketPayload::Literal(2)
+                    },
+                    Packet {
+                        version: 1,
+                        payload: PacketPayload::Literal(3)
+                    },
+                ]
+            )
+        }
+    );
+}
+
+#[test]
+fn test_sum_version_numbers() {
+    let transmissions = [
+        "8A004A801A8002F478",
+        "620080001611562C8802118E34",
+        "C0015000016115A2E0802F182340",
+        "A0016C880162017C3686B18A3D4780",
+    ];
+    let mut iter = transmissions
+        .iter()
+        .map(|t| sum_version_numbers(&t.parse().unwrap()));
+    assert_eq!(iter.next(), Some(16));
+    assert_eq!(iter.next(), Some(12));
+    assert_eq!(iter.next(), Some(23));
+    assert_eq!(iter.next(), Some(31));
+}
+
+#[test]
+fn test_sum_operator() {
+    let packet: Packet = "C200B40A82".parse().unwrap();
+    assert_eq!(eval_packet(&packet), 3);
+}
+
+#[test]
+fn test_product_operator() {
+    let packet: Packet = "04005AC33890".parse().unwrap();
+    assert_eq!(eval_packet(&packet), 54);
+}
+
+#[test]
+fn test_minimum_operator() {
+    let packet: Packet = "880086C3E88112".parse().unwrap();
+    assert_eq!(eval_packet(&packet), 7);
+}
+
+#[test]
+fn test_maximum_operator() {
+    let packet: Packet = "CE00C43D881120".parse().unwrap();
+    assert_eq!(eval_packet(&packet), 9);
+}
+
+#[test]
+fn test_less_than_operator() {
+    let packet: Packet = "D8005AC2A8F0".parse().unwrap();
+    assert_eq!(eval_packet(&packet), 1);
+}
+
+#[test]
+fn test_greater_than_operator() {
+    let packet: Packet = "F600BC2D8F".parse().unwrap();
+    assert_eq!(eval_packet(&packet), 0);
+}
+
+#[test]
+fn test_equal_operator() {
+    let packet: Packet = "9C005AC2F8F0".parse().unwrap();
+    assert_eq!(eval_packet(&packet), 0);
+}
+
+#[test]
+fn test_nested_equal_operator() {
+    let packet: Packet = "9C0141080250320F1802104A08".parse().unwrap();
+    assert_eq!(eval_packet(&packet), 1);
+}