Day 3 part 2

Dependencies

• [2] XBZHQ672 Day 1 solution

Change contents

• file addition: day3p2.rs (----------)
  [2.7]
  + use std::f64;

  + use std::i64;

  + use std::env;

  + use std::collections::HashMap;

  +

  + fn spiral_ring(c: i64) -> i64 {

  + let f = c as f64;

  + ((f.sqrt() + 1.0) / 2.0).ceil() as i64

  + }

  +

  + fn ring_diagonals(n: i64) -> [i64; 4] {

  + let s = (n * 2 - 1).pow(2);

  + let d = n - 1;

  + [s - 6 * d, s - 4 * d, s - 2 * d, s]

  + }

  +

  + fn spiral_coords(c: i64) -> (i64, i64) {

  + let n = spiral_ring(c);

  + let d = ring_diagonals(n);

  + let md = n - 1;

  + for i in [0,1,2,3].iter() {

  + if d[*i] >= c {

  + match *i {

  + 0 => return (md, c + md - d[*i]),

  + 1 => return (d[*i] - md - c, md),

  + 2 => return (-md, d[*i] - md - c),

  + 3 => return (md + c - d[*i], -md),

  + _ => panic!("Index larger than array!")

  + }

  + }

  + }

  + panic!("Unreachable")

  + }

  +

  + fn main() {

  + let args : Vec<String> = env::args().collect();

  + match i64::from_str_radix(&args[1], 10) {

  + Result::Ok(c) => {

  + let mut m = HashMap::new();

  + m.insert((0,0),1);

  + let mut i = 2;

  + loop {

  + let (x,y) = spiral_coords(i);

  + let neighbours = [

  + (x+1,y), (x+1,y+1), (x,y+1), (x-1,y+1),

  + (x-1,y), (x-1,y-1), (x,y-1), (x+1,y-1)

  + ];

  + let mut sum = 0;

  + for n in neighbours.iter() {

  + sum += match m.get(n) {

  + Some(ex) => *ex,

  + None => 0

  + }

  + }

  + m.insert((x,y),sum);

  + if sum > c {

  + println!("{}", sum);

  + break;

  + }

  + i += 1;

  + }

  + },

  + Result::Err(e) => println!("{}", e),

  + }

  + }