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fn main() {
let input = advent::read_lines(3);
println!("3a: {}", power_consumption(&input));
println!("3b: {}", life_support_rating(&input));
}
fn power_consumption<T: AsRef<str>>(input: &[T]) -> u32 {
let bits = count_ones(input);
let gamma = rate(&bits, input.len(), true);
let epsilon = rate(&bits, input.len(), false);
gamma * epsilon
}
fn count_ones_at_pos<T: AsRef<str>>(input: &[T], pos: usize) -> usize {
input.iter()
.filter(|&x| x.as_ref().chars().nth(pos).unwrap() == '1')
.count()
}
fn count_ones<T: AsRef<str>>(input: &[T]) -> Vec<usize> {
input[0].as_ref()
.chars()
.enumerate()
.map(|(i, _)| count_ones_at_pos(input, i))
.collect()
}
fn rate(bits: &[usize], max_count: usize, gamma: bool) -> u32 {
let mut result = 0;
let max_count = max_count;
for count in bits.iter() {
result <<= 1;
if gamma && 2 * count > max_count {
result += 1;
}
if !gamma && 2 * count < max_count {
result += 1;
}
}
result
}
fn life_support_rating<T: AsRef<str>>(input: &[T]) -> usize {
let oxygen = oxygen_rating(input);
let co2 = co2_rating(input);
oxygen * co2
}
fn co2_rating<T: AsRef<str>>(input: &[T]) -> usize {
rating(input, false)
}
fn oxygen_rating<T: AsRef<str>>(input: &[T]) -> usize {
rating(input, true)
}
fn rating<T: AsRef<str>>(input: &[T], oxygen: bool) -> usize {
let mut numbers = vec!["0"; input.len()];
for (i, number) in input.iter().enumerate() {
numbers[i] = number.as_ref();
}
let len = numbers[0].len();
for i in 0 .. len {
let ones = count_ones_at_pos(&numbers, i);
let keep = if (oxygen && 2 * ones >= numbers.len()) || (!oxygen && 2 * ones < numbers.len()) {
'1'
} else {
'0'
};
numbers = numbers.iter()
.filter(|&x| x.chars().nth(i).unwrap() == keep)
.copied()
.collect();
if numbers.len() == 1 {
break;
}
}
usize::from_str_radix(numbers[0], 2).unwrap()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = [
"00100",
"11110",
"10110",
"10111",
"10101",
"01111",
"00111",
"11100",
"10000",
"11001",
"00010",
"01010",
];
assert_eq!(power_consumption(&input), 198);
assert_eq!(life_support_rating(&input), 230);
}
}
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