Add solution to part 2 of day 1

This commit is contained in:
Wesley Moore 2017-12-03 09:02:11 +10:00
parent a89cdfc860
commit b35039cb2f
2 changed files with 65 additions and 4 deletions

View file

@ -7,3 +7,17 @@ For example:
1234 produces 0 because no digit matches the next.
91212129 produces 9 because the only digit that matches the next one is the last digit, 9.
--- Part Two ---
You notice a progress bar that jumps to 50% completion. Apparently, the door isn't yet satisfied, but it did emit a star as encouragement. The instructions change:
Now, instead of considering the next digit, it wants you to consider the digit halfway around the circular list. That is, if your list contains 10 items, only include a digit in your sum if the digit 10/2 = 5 steps forward matches it. Fortunately, your list has an even number of elements.
For example:
1212 produces 6: the list contains 4 items, and all four digits match the digit 2 items ahead.
1221 produces 0, because every comparison is between a 1 and a 2.
123425 produces 4, because both 2s match each other, but no other digit has a match.
123123 produces 12.
12131415 produces 4.

View file

@ -7,6 +7,7 @@ fn main() {
file.read_to_end(&mut input).expect("error reading input");
println!("{}", captcha(&input));
println!("{}", captcha2(&input));
}
fn captcha(input: &[u8]) -> u64 {
@ -24,27 +25,73 @@ fn captcha(input: &[u8]) -> u64 {
sum
}
fn captcha2(input: &[u8]) -> u64 {
let digits = input.iter()
.take_while(|&&chr| chr >= 0x30 && chr <= 0x39)
.collect::<Vec<_>>();
let mut sum = 0;
for idx in 0..digits.len() {
if digits[idx] == digits[(idx + (digits.len() / 2)) % digits.len()] {
sum += *digits[idx] as u64 - 0x30;
}
}
sum
}
// 1122 produces a sum of 3 (1 + 2) because the first digit (1) matches the second digit and the
// third digit (2) matches the fourth digit.
#[test]
fn test_example1() {
fn test_captcha_example1() {
assert_eq!(captcha(b"1122"), 3);
}
// 1111 produces 4 because each digit (all 1) matches the next.
#[test]
fn test_example2() {
fn test_captcha_example2() {
assert_eq!(captcha(b"1111"), 4);
}
// 1234 produces 0 because no digit matches the next.
#[test]
fn test_example3() {
fn test_captcha_example3() {
assert_eq!(captcha(b"1234"), 0);
}
// 91212129 produces 9 because the only digit that matches the next one is the last digit, 9.
#[test]
fn test_example4() {
fn test_captcha_example4() {
assert_eq!(captcha(b"91212129"), 9);
}
// 1212 produces 6: the list contains 4 items, and all four digits match the digit 2 items ahead.
#[test]
fn test_captcha2_example1() {
assert_eq!(captcha2(b"1212"), 6);
}
// 1221 produces 0, because every comparison is between a 1 and a 2.
#[test]
fn test_captcha2_example2() {
assert_eq!(captcha2(b"1221"), 0);
}
// 123425 produces 4, because both 2s match each other, but no other digit has a match.
#[test]
fn test_captcha2_example3() {
assert_eq!(captcha2(b"123425"), 4);
}
// 123123 produces 12.
#[test]
fn test_captcha2_example4() {
assert_eq!(captcha2(b"123123"), 12);
}
// 12131415 produces 4.
#[test]
fn test_captcha2_example5() {
assert_eq!(captcha2(b"12131415"), 4);
}