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Reimplement day 14 with infinite streams.

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Bert Peters
2018-12-14 14:41:56 +01:00
parent ccdbea4a1c
commit bcccc85073
1 changed files with 47 additions and 41 deletions
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88
2018/src/day14.rs
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@@ -1,25 +1,50 @@
use std::io::Read; use std::io::Read;
use common::Solution;
use common::read_single_input; use common::read_single_input;
use common::Solution;
struct ResultStream {
elves: [usize; 2],
state: Vec<u8>,
next: usize,
}
impl ResultStream {
pub fn new() -> Self {
ResultStream {
elves: [0, 1],
state: vec![3, 7],
next: 0,
}
}
}
impl Iterator for ResultStream {
type Item = u8;
fn next(&mut self) -> Option<<Self as Iterator>::Item> {
let state = &mut self.state;
if self.next == state.len() {
let elves = &mut self.elves;
let n = state[elves[0]] + state[elves[1]];
if n >= 10 {
state.push(1);
}
state.push(n % 10);
elves[0] = (elves[0] + 1 + state[elves[0]] as usize) % state.len();
elves[1] = (elves[1] + 1 + state[elves[1]] as usize) % state.len();
};
let n = Some(state[self.next]);
self.next += 1;
n
}
}
fn skill_after(n: usize) -> u64 { fn skill_after(n: usize) -> u64 {
let mut state = vec![3u8, 7]; let state = ResultStream::new();
let mut elves = [0, 1];
while state.len() < n + 10 {
let result = state[elves[0]] + state[elves[1]];
if result >= 10 {
state.push(result / 10);
}
state.push(result % 10);
elves[0] = (elves[0] + state[elves[0]] as usize + 1) % state.len();
elves[1] = (elves[1] + state[elves[1]] as usize + 1) % state.len();
}
let mut skill = 0; let mut skill = 0;
for d in state.into_iter().skip(n).take(10) { for d in state.skip(n).take(10) {
skill *= 10; skill *= 10;
skill += d as u64; skill += d as u64;
} }
@@ -27,37 +52,18 @@ fn skill_after(n: usize) -> u64 {
skill skill
} }
fn update_current(mut current: usize, by: usize, base: usize) -> usize {
current *= 10;
current %= base;
current += by;
current
}
fn find_first(n: usize, len: usize) -> usize { fn find_first(n: usize, len: usize) -> usize {
let mut state = vec![3u8, 7];
let mut elves = [0, 1];
let mut current = 37;
let mod_base = 10usize.pow(len as u32); let mod_base = 10usize.pow(len as u32);
let mut current = 0;
loop { for (i, b) in ResultStream::new().enumerate() {
let result = state[elves[0]] + state[elves[1]]; current = (current * 10) % mod_base;
if result >= 10 { current += b as usize;
current = update_current(current, result as usize / 10, mod_base);
if current == n {
return state.len() - len + 1;
}
state.push(result / 10);
}
current = update_current(current, result as usize % 10, mod_base);
if current == n { if current == n {
return state.len() - len + 1; return i - len + 1;
} }
state.push(result % 10);
elves[0] = (elves[0] + state[elves[0]] as usize + 1) % state.len();
elves[1] = (elves[1] + state[elves[1]] as usize + 1) % state.len();
} }
unreachable!();
} }