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91 lines
2.3 KiB
91 lines
2.3 KiB
use std::collections::HashMap;
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use std::iter;
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use failure::*;
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#[allow(dead_code)]
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pub fn solve(input: &str) -> Result<String, Error> {
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let input: usize = input.trim().parse()?;
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// 1
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// spiral()
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// .zip(1..)
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// .find(|&(_, i)| i == (square - 1))
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// .map(|(coord, _)| (coord.0 + coord.1).to_string())
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// .ok_or_else(|| format_err!(""))
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// 2
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let mut grid = HashMap::new();
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grid.insert(Coord(0, 0), 1);
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spiral()
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.map(|coord| {
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let sum = coord.neighbors().iter().filter_map(|x| grid.get(x)).sum();
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grid.insert(coord, sum);
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sum
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})
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.find(|value| value > &input)
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.map(|value| value.to_string())
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.ok_or_else(|| err_msg(""))
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}
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#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
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struct Coord(isize, isize);
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impl Coord {
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#[allow(dead_code)]
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fn neighbors(&self) -> Vec<Coord> {
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vec![
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[-1, 1],
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[0, 1],
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[1, 1],
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[-1, 0],
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[1, 0],
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[-1, -1],
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[0, -1],
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[1, -1],
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].iter()
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.map(|delta| Coord(self.0 + delta[0], self.1 + delta[1]))
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.collect()
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}
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}
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#[derive(Clone, Copy, Debug, PartialEq)]
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enum Dir {
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Right,
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Up,
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Left,
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Down,
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}
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#[allow(dead_code)]
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lazy_static! {
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static ref DIRS: Vec<Dir> = vec![Dir::Right, Dir::Up, Dir::Left, Dir::Down];
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}
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#[allow(dead_code)]
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fn spiral() -> impl Iterator<Item = Coord> {
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(1..)
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.flat_map(|x| iter::repeat(x).take(2))
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.zip(DIRS.iter().cycle())
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.flat_map(|(steps, dir)| iter::repeat(dir).take(steps))
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.scan(Coord(0, 0), |state, &dir| {
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*state = match dir {
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Dir::Right => Coord(state.0 + 1, state.1),
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Dir::Up => Coord(state.0, state.1 + 1),
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Dir::Left => Coord(state.0 - 1, state.1),
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Dir::Down => Coord(state.0, state.1 - 1),
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};
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Some(*state)
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})
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}
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#[test]
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fn test_coords() {
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let mut spiral = spiral();
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assert_eq!(spiral.next(), Some(Coord(1, 0)));
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assert_eq!(spiral.next(), Some(Coord(1, 1)));
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assert_eq!(spiral.next(), Some(Coord(0, 1)));
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assert_eq!(spiral.next(), Some(Coord(-1, 1)));
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assert_eq!(spiral.next(), Some(Coord(-1, 0)));
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assert_eq!(spiral.next(), Some(Coord(-1, -1)));
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}
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