Advent of Code 2019
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use std::io::BufRead;
use std::str::FromStr;
use std::num::ParseIntError;
use std::fmt::{self, Display};
use std::collections::{HashSet, HashMap};
use Segment::*;
#[derive(Debug, PartialEq)]
enum Segment {
Up(i32),
Down(i32),
Right(i32),
Left(i32),
}
enum SegmentError {
UnknownDirection(char),
ParseIntError(ParseIntError)
}
impl Display for SegmentError {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
match *self {
SegmentError::UnknownDirection(direction) => write!(f, "Unknown direction `{}`", direction),
SegmentError::ParseIntError(ref e) => e.fmt(f),
}
}
}
impl FromStr for Segment {
type Err = SegmentError;
fn from_str(s: &str) -> Result<Self, Self::Err> {
let direction = s.chars().next().unwrap();
let length = s[1..].parse().map_err(|e| SegmentError::ParseIntError(e))?;
let segment = match direction {
'U' => Up(length),
'D' => Down(length),
'R' => Right(length),
'L' => Left(length),
direction => {
return Err(SegmentError::UnknownDirection(direction));
}
};
Ok(segment)
}
}
impl Segment {
#[inline]
fn direction(&self) -> (i32, i32) {
match self {
Up(_) => (0, 1),
Down(_) => (0, -1),
Right(_) => (1, 0),
Left(_) => (-1, 0),
}
}
#[inline]
fn length(&self) -> i32 {
match self {
Up(l) | Down(l) | Right(l) | Left(l) => *l
}
}
}
fn parse_input<F: BufRead> (input: &mut F) -> Vec<Segment> {
let mut buf = String::new();
let _num_bytes = input.read_line(&mut buf).expect("Unable to read a line of input file");
buf.trim().split(",").filter_map(|segment| segment.parse().ok()).collect()
}
pub fn part1<F: BufRead> (mut input: F) {
let path1 = parse_input(&mut input);
let path2 = parse_input(&mut input);
let res = compute_closest_intersection(path1, path2);
println!("{}", res);
}
fn compute_closest_intersection(path1: Vec<Segment>, path2: Vec<Segment>) -> i32 {
let steps1 = build_full_path(path1, 0, (0, 0), HashMap::new(), 1);
let steps2 = build_full_path(path2, 0, (0, 0), HashMap::new(), 1);
let seen1: HashSet<_> = steps1.keys().collect();
let seen2: HashSet<_> = steps2.keys().collect();
seen1.intersection(&seen2).map(|(x, y)| x.abs() + y.abs()).min().unwrap()
}
pub fn part2<F: BufRead> (mut input: F) {
let path1 = parse_input(&mut input);
let path2 = parse_input(&mut input);
let res = compute_first_intersection(path1, path2);
println!("{}", res);
}
fn compute_first_intersection(path1: Vec<Segment>, path2: Vec<Segment>) -> i32 {
let steps1 = build_full_path(path1, 0, (0, 0), HashMap::new(), 1);
let steps2 = build_full_path(path2, 0, (0, 0), HashMap::new(), 1);
let seen1: HashSet<_> = steps1.keys().collect();
let seen2: HashSet<_> = steps2.keys().collect();
seen1.intersection(&seen2).map(|coord| steps1[coord] + steps2[coord]).min().unwrap()
}
fn build_full_path(
path: Vec<Segment>,
index: usize,
(x0, y0): (i32, i32),
mut steps: HashMap<(i32, i32), i32>,
current_step: i32
) -> HashMap<(i32, i32), i32> {
if index == path.len() {
steps
} else {
let segment = &path[index];
let (dx, dy) = segment.direction();
let length = segment.length();
let mut current_step = current_step;
for i in 1..(length + 1) {
steps.entry((x0 + i * dx, y0 + i * dy)).or_insert(current_step);
current_step += 1;
}
build_full_path(path, index + 1, (x0 + length * dx, y0 + length * dy), steps, current_step)
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_input_parsing() {
let mut input = "U7,R6,D4,L4\n".as_bytes();
let expected = vec![Up(7), Right(6), Down(4), Left(4)];
let res = parse_input(&mut input);
assert_eq!(res, expected);
}
#[test]
fn test_compute_closest_intersection() {
let mut input = r#"R8,U5,L5,D3
U7,R6,D4,L4
R75,D30,R83,U83,L12,D49,R71,U7,L72
U62,R66,U55,R34,D71,R55,D58,R83
R98,U47,R26,D63,R33,U87,L62,D20,R33,U53,R51
U98,R91,D20,R16,D67,R40,U7,R15,U6,R7
"#.as_bytes();
let test_results = [6, 159, 135];
for expected in &test_results {
let path1 = parse_input(&mut input);
let path2 = parse_input(&mut input);
let res = compute_closest_intersection(path1, path2);
assert_eq!(res, *expected)
}
}
#[test]
fn test_compute_first_intersection() {
let mut input = r#"R8,U5,L5,D3
U7,R6,D4,L4
R75,D30,R83,U83,L12,D49,R71,U7,L72
U62,R66,U55,R34,D71,R55,D58,R83
R98,U47,R26,D63,R33,U87,L62,D20,R33,U53,R51
U98,R91,D20,R16,D67,R40,U7,R15,U6,R7
"#.as_bytes();
let test_results = [30, 610, 410];
for expected in &test_results {
let path1 = parse_input(&mut input);
let path2 = parse_input(&mut input);
let res = compute_first_intersection(path1, path2);
assert_eq!(res, *expected)
}
}
}