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use std::collections::{HashMap};
use std::io::{BufRead};
pub fn ascii_to_u64(s: & [u8]) -> u64 {
#[cfg(debug_assertions)]
{
assert!(s.into_iter().all(|& c| c.is_ascii_digit()), "Not an ASCII base-10 number");
}
// SAFETY: AoC is ASCII-only.
unsafe { std::str::from_utf8_unchecked(s) }.parse().unwrap()
}
pub fn is_all_ascii_ws<'a, I: IntoIterator<Item = &'a u8>>(s: I) -> bool {
s.into_iter().all(|& c| c.is_ascii_whitespace())
}
pub fn read_helper<'a, 'b, R: BufRead>(r: &'a mut R, buf: &'b mut Vec<u8>, token: u8) -> std::io::Result<usize> {
buf.clear();
let num_bytes = r.read_until(token, buf)?;
if buf.last() == Some(& token) { buf.pop(); }
Ok(num_bytes)
}
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum Direction {
L, R
}
impl TryFrom<u8> for Direction {
type Error = &'static str;
fn try_from(c: u8) -> Result<Self, Self::Error> {
match c {
b'L' => Ok(Self::L),
b'R' => Ok(Self::R),
_ => Err("ASCII character not a valid direction")
}
}
}
pub type Node = [u8; 3];
pub fn gcd(mut m: u64, mut n: u64) -> u64 {
if m < n {
std::mem::swap(&mut m, &mut n);
}
while n > 0 {
let r: u64 = m % n;
m = n;
n = r;
}
m
}
pub fn lcm(m: u64, n: u64) -> u64 {
m*(n/gcd(m, n))
}
pub fn walk<'a, I, F>(start: Node, is_finish: F, map: & HashMap<Node, (Node, Node)>, instructions: I) -> usize
where I: IntoIterator<Item = &'a Direction>,
<I as IntoIterator>::IntoIter: Clone,
F: Fn(Node) -> bool {
let mut node: Node = start;
for (i, instruction) in instructions.into_iter().cycle().enumerate() {
if is_finish(node) {
return i;
}
let (left, right) = map.get(& node).expect("Non-existent node");
match instruction {
Direction::L => { node = *left; },
Direction::R => { node = *right; }
}
}
unreachable!("Non-terminating map")
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_gcd() {
assert_eq!(gcd(1238124652, 22146), 2);
}
#[test]
fn test_gcd_2() {
assert_eq!(gcd(5025124, 1040), 52);
}
#[test]
fn test_gcd_3() {
assert_eq!(gcd(1040, 5025124), 52);
}
#[test]
fn test_lcm() {
assert_eq!(lcm(1040, 5025124), 100502480);
}
}
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