2021 day3/rust: add solution

This commit is contained in:
Xiretza 2021-12-04 12:17:44 +01:00
parent 697377c22d
commit ba68214754
2 changed files with 66 additions and 0 deletions

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[package]
name = "day3_rs"
version = "0.1.0"
edition = "2021"
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
[dependencies]

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#![warn(clippy::pedantic)]
use std::io::{stdin, BufRead};
fn find_rating(num_bits: usize, mut range: &[usize], keep_most_common_bit: bool) -> usize {
for idx in (0..num_bits).rev() {
if range.len() == 1 {
break;
}
let nth_bit = |x| x >> idx & 1;
let partition_point = range.iter().position(|&n| nth_bit(n) == 1).unwrap();
let center_bit = nth_bit(range[range.len() / 2]);
let keep_first_half = if keep_most_common_bit {
center_bit == 0
} else {
center_bit == 1
};
if keep_first_half {
range = &range[..partition_point];
} else {
range = &range[partition_point..];
}
}
range[0]
}
fn main() {
let lines: Vec<_> = stdin().lock().lines().map(Result::unwrap).collect();
let num_bits = lines[0].len();
let gamma: usize = (0..num_bits)
.map(|i| {
lines
.iter()
.filter(|line| line.chars().nth(i).unwrap() == '1')
.count()
})
.map(|n| if n > lines.len() / 2 { 1 } else { 0 })
.reduce(|accum, bit| accum << 1 | bit)
.unwrap();
let sigma = !gamma & ((1 << num_bits) - 1);
println!("{}", gamma * sigma);
let mut numbers: Vec<_> = lines
.iter()
.map(|n| usize::from_str_radix(n, 2).unwrap())
.collect();
numbers.sort_unstable();
let oxygen = find_rating(num_bits, &numbers, true);
let co2 = find_rating(num_bits, &numbers, false);
println!("{}", oxygen * co2);
}