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main.rs
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main.rs
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use std::io::{self, BufRead};
use anyhow::{Context, Result};
#[derive(Debug)]
enum Node {
Literal {
version: u8,
type_id: u8,
value: u128,
},
Operator {
version: u8,
type_id: u8,
nodes: Vec<Node>,
},
}
type Data = Vec<char>;
// (Node, consumed)
fn parse(data: &Data) -> Result<(Node, u32)> {
let type_id = u8::from_str_radix(&data[3..=5].iter().collect::<String>(), 2)
.context(format!("invalid version, data: {:?}", data))?;
match type_id {
4 => parse_literal(&data),
_ => parse_operator(&data),
}
}
fn parse_literal(data: &Data) -> Result<(Node, u32)> {
let version = u8::from_str_radix(&data[0..=2].iter().collect::<String>(), 2)
.context(format!("invalid header, data: {:?}", data))?;
let mut value_data: Vec<char> = Vec::new();
let mut data_i = 6;
loop {
for j in data_i + 1..data_i + 5 {
value_data.push(data[j]);
}
if data[data_i] == '0' {
break;
}
data_i += 5;
}
let value = u128::from_str_radix(&value_data.iter().collect::<String>(), 2)
.context(format!("invalid value, value_data: {:?}", value_data))?;
Ok((
Node::Literal {
version,
type_id: 4,
value,
},
data_i as u32 + 5,
))
}
fn parse_operator(data: &Data) -> Result<(Node, u32)> {
let mut consumed: u32 = 0;
// header
let version = u8::from_str_radix(&data[0..=2].iter().collect::<String>(), 2)
.context(format!("invalid header, data: {:?}", data))?;
let type_id = u8::from_str_radix(&data[3..=5].iter().collect::<String>(), 2)
.context(format!("invalid version, data: {:?}", data))?;
consumed += 6;
// length_type_id: 0(sub packets bits, 15bit length), 1(packets num, 11bit length)
let length_type_id = data[consumed as usize];
consumed += 1;
// sub-packets length
let length_bits = if length_type_id == '0' { 15 } else { 11 };
let sub_packet_length = u32::from_str_radix(
&data[consumed as usize..(consumed + length_bits) as usize]
.iter()
.collect::<String>(),
2,
)
.context(format!("invalid length format, data: {:?}", data))?;
consumed += length_bits;
// sub-packets
let mut nodes: Vec<Node> = Vec::new();
let mut sub_packet_consumed: u32 = 0;
loop {
let (node, consumed) = parse(&data[(consumed + sub_packet_consumed) as usize..].to_vec())?;
nodes.push(node);
sub_packet_consumed += consumed;
if length_type_id == '0' {
if sub_packet_consumed >= sub_packet_length {
break;
}
} else {
if nodes.len() >= sub_packet_length as usize {
break;
}
}
}
consumed += sub_packet_consumed;
Ok((
Node::Operator {
version,
type_id,
nodes,
},
consumed,
))
}
fn eval(node: &Node) -> Result<u128> {
match node {
Node::Literal {
version: _,
type_id: _,
value,
} => Ok(*value as u128),
Node::Operator {
version: _,
type_id,
nodes,
} => {
let reduce = |f: fn(x: u128, y: u128) -> u128| -> u128 {
nodes
.iter()
.map(|node| eval(node).unwrap())
.reduce(f)
.unwrap()
};
let reduce_bool = |f: fn(x: u128, y: u128) -> bool| -> u128 {
let n1 = eval(&nodes[0]).unwrap();
let n2 = eval(&nodes[1]).unwrap();
if f(n1, n2) {
1
} else {
0
}
};
match type_id {
0 => Ok(reduce(|x, y| x + y)),
1 => Ok(reduce(|x, y| x * y)),
2 => Ok(reduce(|x, y| if x < y { x } else { y })),
3 => Ok(reduce(|x, y| if x > y { x } else { y })),
5 => Ok(reduce_bool(|x, y| x > y)),
6 => Ok(reduce_bool(|x, y| x < y)),
7 => Ok(reduce_bool(|x, y| x == y)),
_ => Err(anyhow::anyhow!(format!("unknown type_id: {}", type_id))),
}
}
}
}
fn main() {
let stdin = io::stdin();
let line = stdin.lock().lines().next().unwrap().unwrap();
let mut data = Data::new();
for char in line.chars() {
let num = u8::from_str_radix(&char.to_string(), 16).unwrap();
for i in 0..=3 {
if 1 << (3 - i) & num != 0 {
data.push('1');
} else {
data.push('0');
}
}
}
let (node, _) = parse(&data).unwrap();
println!("ans {}", eval(&node).unwrap());
}