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use std::collections::{HashMap, VecDeque};
use std::io::{self, Read};
#[derive(Clone, Copy, PartialEq, Eq, Hash)]
struct Point {
x: u32,
y: u32,
}
const START: Point = Point { x: 1, y: 1 };
impl Point {
fn north(self) -> Option<Point> {
if self.y == 0 {
None
} else {
Some(Point { x: self.x, y: self.y - 1 })
}
}
fn east(self) -> Point {
Point { x: self.x + 1, y: self.y }
}
fn south(self) -> Point {
Point { x: self.x, y: self.y + 1 }
}
fn west(self) -> Option<Point> {
if self.x == 0 {
None
} else {
Some(Point { x: self.x - 1, y: self.y })
}
}
fn neighbors(self) -> [Option<Point>; 4] {
[self.north(), Some(self.east()), Some(self.south()), self.west()]
}
}
#[derive(Clone, Copy)]
struct Layout {
constant: u32,
}
impl Layout {
fn is_open(&self, point: Point) -> bool {
let Point { x, y } = point;
let sum = x * x + 3 * x + 2 * x * y + y + y * y + self.constant;
sum.count_ones() % 2 == 0
}
}
fn solve1(goal: Point, constant: u32) -> u32 {
let layout = Layout { constant: constant };
let mut distance = HashMap::new();
let mut frontier = VecDeque::new();
frontier.push_back(START);
distance.insert(START, 0);
while let Some(current) = frontier.pop_front() {
if current == goal { break; }
let current_distance = *distance.get(¤t).unwrap();
let neighbors = current.neighbors();
let iter = neighbors.iter()
.filter_map(|&p| p)
.filter(|&p| layout.is_open(p));
for next in iter {
if !distance.contains_key(&next) {
frontier.push_back(next);
distance.insert(next, current_distance + 1);
}
}
}
*distance.get(&goal).unwrap()
}
fn solve2(limit: u32, constant: u32) -> usize {
let layout = Layout { constant: constant };
let mut distance = HashMap::new();
let mut frontier = VecDeque::new();
frontier.push_back(START);
distance.insert(START, 0);
while let Some(current) = frontier.pop_front() {
let current_distance = *distance.get(¤t).unwrap();
if current_distance == limit { continue; }
let neighbors = current.neighbors();
let iter = neighbors.iter()
.filter_map(|&p| p)
.filter(|&p| layout.is_open(p));
for next in iter {
if !distance.contains_key(&next) {
frontier.push_back(next);
distance.insert(next, current_distance + 1);
}
}
}
distance.len()
}
fn main() {
let mut input = String::new();
io::stdin().read_to_string(&mut input).unwrap();
println!("Part 1: {}", solve1(Point { x: 31, y: 39 }, input.trim().parse().unwrap()));
println!("Part 2: {}", solve2(50, input.trim().parse().unwrap()));
}
#[test]
fn part1() {
assert_eq!(11, solve1(Point { x: 7, y: 4 }, 10));
}
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