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refactor in preparation for part 2

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This commit is contained in:
Joseph Montanaro 2021-12-03 14:48:34 -08:00
parent b519e0bad2
commit b1a8ab8bcd
1 changed files with 15 additions and 4 deletions
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19
2021/src/day3.rs
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@ -1,7 +1,7 @@
use color_eyre::eyre; use color_eyre::eyre;
pub fn part1(numbers: &Vec<u16>) -> u64 { fn most_common_bits(numbers: &Vec<u16>) -> u16 {
let mut bit_diffs: [isize; 12] = [0; 12]; let mut bit_diffs: [isize; 12] = [0; 12];
for num in numbers { for num in numbers {
for i in 0..11 { for i in 0..11 {
@ -14,13 +14,24 @@ pub fn part1(numbers: &Vec<u16>) -> u64 {
} }
} }
let mut gamma = 0u16; let mut result = 0u16;
for (i, sum) in bit_diffs.iter().enumerate() { for (i, sum) in bit_diffs.iter().enumerate() {
let bit = if *sum >= 0 {1} else {0}; let bit = if *sum >= 0 {1} else {0};
gamma |= bit << i; result |= bit << i;
} }
let epsilon = !gamma & (65535 >> 4); // since these are really only 12-bit numbers we have to clear the 4 spurious 1's that come from inverting epsilon result
}
fn invert_12bit(n: u16) -> u16 {
!n & (65535 >> 4) // since these are really only 12-bit numbers we have to clear the 4 spurious 1's that come from inverting the original
}
fn part1(numbers: &Vec<u16>) -> u64 {
let gamma = most_common_bits(numbers);
let epsilon = invert_12bit(gamma);
epsilon as u64 * gamma as u64 epsilon as u64 * gamma as u64
} }