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use std::fs;
fn solve_part1(lines: &Vec<&str>) -> String {
let mut result = String::new();
let mut num = 5;
for line in lines {
for c in line.chars() {
num = match c {
'U' => if num - 3 > 0 { num - 3 } else { num },
'D' => if num + 3 < 10 { num + 3 } else { num },
'L' => if num % 3 != 1 { num - 1 } else { num },
'R' => if num % 3 != 0 { num + 1 } else { num },
_ => num, // shouldn't happen
}
}
result.push_str(&num.to_string());
}
result
}
fn solve_part2(lines: &Vec<&str>) -> String {
let mut result = String::new();
// Part 2's keypad is a bit more exotic
let keypad = [
[0, 0, 1, 0, 0],
[0, 2, 3, 4, 0],
[5, 6, 7, 8, 9],
[0, 10, 11, 12, 0],
[0, 0, 13, 0, 0],
];
let mut pos = (2, 0); // (row, col) index
for line in lines {
for c in line.chars() {
let mut new = pos;
match c {
'U' => new.0 = if pos.0 > 0 { pos.0 - 1 } else { pos.0 },
'D' => new.0 = if pos.0 < 4 { pos.0 + 1 } else { pos.0 },
'L' => new.1 = if pos.1 > 0 { pos.1 - 1 } else { pos.1 },
'R' => new.1 = if pos.1 < 4 { pos.1 + 1 } else { pos.1 },
_ => {}, // shouldn't happen
};
// Ignore this `c' if it would take us off the diamond's edge
if keypad[new.0][new.1] != 0 {
pos = new;
}
}
// Print as hexadecimal to follow puzzle description
result.push_str(&format!("{:X}", keypad[pos.0][pos.1]));
}
result
}
fn main() {
// Read directions from input text file
let input = fs::read_to_string("input.txt").unwrap();
let lines = input.lines().collect();
// Part 1 gives 74921 for me
println!("Part 1 solution: {}", solve_part1(&lines));
// Part 2 gives A6B35 for me
println!("Part 2 solution: {}", solve_part2(&lines));
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn part1_example1() {
let lines = vec!["ULL", "RRDDD", "LURDL", "UUUUD"];
assert_eq!(solve_part1(&lines), "1985");
}
#[test]
fn part2_example1() {
let lines = vec!["ULL", "RRDDD", "LURDL", "UUUUD"];
assert_eq!(solve_part2(&lines), "5DB3");
}
}
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