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//! # [Day 13: Packet Scanners](http://adventofcode.com/2017/day/13) //! //! You need to cross a vast *firewall*. The firewall consists of several //! layers, each with a *security scanner* that moves back and forth across //! the layer. To succeed, you must not be detected by a scanner. use std::str::FromStr; use std::ops; /// Within each layer, a security scanner moves back and forth within its /// range. Each security scanner starts at the top and moves down until it /// reaches the bottom, then moves up until it reaches the top, and repeats. /// A security scanner takes *one picosecond* to move one step. Drawing /// scanners as `S`, the first few picoseconds look like this: /// /// ```text /// Picosecond 0: /// 0 1 2 3 4 5 6 /// [S] [S] ... ... [S] ... [S] /// [ ] [ ] [ ] [ ] /// [ ] [ ] [ ] /// [ ] [ ] /// /// Picosecond 1: /// 0 1 2 3 4 5 6 /// [ ] [ ] ... ... [ ] ... [ ] /// [S] [S] [S] [S] /// [ ] [ ] [ ] /// [ ] [ ] /// /// Picosecond 2: /// 0 1 2 3 4 5 6 /// [ ] [S] ... ... [ ] ... [ ] /// [ ] [ ] [ ] [ ] /// [S] [S] [S] /// [ ] [ ] /// /// Picosecond 3: /// 0 1 2 3 4 5 6 /// [ ] [ ] ... ... [ ] ... [ ] /// [S] [S] [ ] [ ] /// [ ] [ ] [ ] /// [S] [S] /// ``` #[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)] pub struct Layer { range: usize, position: usize, forward: bool, } impl Layer { fn step(&mut self) { if self.forward { if self.position < self.range - 1 { self.position += 1; } else { self.forward = false; self.position -= 1; } } else { if self.position > 0 { self.position -= 1; } else { self.forward = true; self.position += 1; } } } } impl FromStr for Layer { type Err = ::std::num::ParseIntError; fn from_str(s: &str) -> Result<Self, Self::Err> { Ok(Layer { range: s.parse::<usize>()?, position: 0, forward: true, }) } } #[cfg(test)] #[test] fn test_layers() { let input = "0: 3 1: 2 4: 4 6: 4 "; let mut firewall = Firewall::new(&input); // Picosecond 0 assert_eq!(firewall[0].unwrap().position, 0); assert_eq!(firewall[1].unwrap().position, 0); assert_eq!(firewall[4].unwrap().position, 0); assert_eq!(firewall[6].unwrap().position, 0); // Picosecond 1 firewall.step(); assert_eq!(firewall[0].unwrap().position, 1); assert_eq!(firewall[1].unwrap().position, 1); assert_eq!(firewall[4].unwrap().position, 1); assert_eq!(firewall[6].unwrap().position, 1); // Picosecond 2 firewall.step(); assert_eq!(firewall[0].unwrap().position, 2); assert_eq!(firewall[1].unwrap().position, 0); assert_eq!(firewall[4].unwrap().position, 2); assert_eq!(firewall[6].unwrap().position, 2); // Picosecond 3 firewall.step(); assert_eq!(firewall[0].unwrap().position, 1); assert_eq!(firewall[1].unwrap().position, 1); assert_eq!(firewall[4].unwrap().position, 3); assert_eq!(firewall[6].unwrap().position, 3); } /// By studying the firewall briefly, you are able to record (in your puzzle /// input) the *depth* of each layer and the *range* of the scanning area /// for the scanner within it, written as `depth: range`. Each layer has a /// thickness of exactly `1`. A layer at depth `0` begins immediately inside /// the firewall; a layer at depth `1` would start immediately after that. /// /// For example, suppose you've recorded the following: /// /// ```text /// 0: 3 /// 1: 2 /// 4: 4 /// 6: 4 /// ``` /// /// This means that there is a layer immediately inside the firewall (with /// range `3`), a second layer immediately after that (with range `2`), a /// third layer which begins at depth `4` (with range `4`), and a fourth /// layer which begins at depth 6 (also with range `4`). Visually, it might /// look like this: /// /// ```text /// 0 1 2 3 4 5 6 /// [ ] [ ] ... ... [ ] ... [ ] /// [ ] [ ] [ ] [ ] /// [ ] [ ] [ ] /// [ ] [ ] /// ``` #[derive(Clone, PartialEq, Eq, Debug, Hash)] pub struct Firewall(Vec<Option<Layer>>); impl Firewall { fn new(input: &str) -> Firewall { Firewall( input.lines() .fold(Vec::new(), |mut firewall, line| { let mut vals = line.split(": "); let depth: usize = vals.next().map(FromStr::from_str).unwrap().unwrap(); let layer = vals.next().map(FromStr::from_str).unwrap().unwrap(); if firewall.len() < depth + 1 { firewall.resize(depth + 1, None); } firewall[depth] = Some(layer); firewall }) ) } fn len(&self) -> usize { self.0.len() } pub fn step(&mut self) { for layer in &mut self.0 { layer.iter_mut().for_each(|x| x.step()); } } } impl ops::Index<usize> for Firewall { type Output = Option<Layer>; fn index(&self, i: usize) -> &Self::Output { &self.0[i] } } impl ops::IndexMut<usize> for Firewall { fn index_mut(&mut self, i: usize) -> &mut Self::Output { &mut self.0[i] } } #[cfg(test)] #[test] fn test_firewall() { let input = "0: 3 1: 2 4: 4 6: 4 "; let firewall = Firewall::new(&input); assert_eq!(firewall.len(), 7); assert_eq!(firewall[0].unwrap().range, 3); assert_eq!(firewall[1].unwrap().range, 2); assert_eq!(firewall[2], None); assert_eq!(firewall[3], None); assert_eq!(firewall[4].unwrap().range, 4); assert_eq!(firewall[5], None); assert_eq!(firewall[6].unwrap().range, 4); } /// Your plan is to hitch a ride on a packet about to move through the /// firewall. The packet will travel along the top of each layer, and it /// moves at *one layer per picosecond*. Each picosecond, the packet moves /// one layer forward (its first move takes it into layer 0), and then the /// scanners move one step. If there is a scanner at the top of the layer /// *as your packet enters it*, you are *caught*. (If a scanner moves into /// the top of its layer while you are there, you are *not* caught: it /// doesn't have time to notice you before you leave.) If you were to do /// this in the configuration above, marking your current position with /// parentheses, your passage through the firewall would look like this: /// /// ```text /// Initial state: /// 0 1 2 3 4 5 6 /// [S] [S] ... ... [S] ... [S] /// [ ] [ ] [ ] [ ] /// [ ] [ ] [ ] /// [ ] [ ] /// /// Picosecond 0: /// 0 1 2 3 4 5 6 /// (S) [S] ... ... [S] ... [S] /// [ ] [ ] [ ] [ ] /// [ ] [ ] [ ] /// [ ] [ ] /// /// 0 1 2 3 4 5 6 /// ( ) [ ] ... ... [ ] ... [ ] /// [S] [S] [S] [S] /// [ ] [ ] [ ] /// [ ] [ ] /// /// /// Picosecond 1: /// 0 1 2 3 4 5 6 /// [ ] ( ) ... ... [ ] ... [ ] /// [S] [S] [S] [S] /// [ ] [ ] [ ] /// [ ] [ ] /// /// 0 1 2 3 4 5 6 /// [ ] (S) ... ... [ ] ... [ ] /// [ ] [ ] [ ] [ ] /// [S] [S] [S] /// [ ] [ ] /// /// /// Picosecond 2: /// 0 1 2 3 4 5 6 /// [ ] [S] (.) ... [ ] ... [ ] /// [ ] [ ] [ ] [ ] /// [S] [S] [S] /// [ ] [ ] /// /// 0 1 2 3 4 5 6 /// [ ] [ ] (.) ... [ ] ... [ ] /// [S] [S] [ ] [ ] /// [ ] [ ] [ ] /// [S] [S] /// /// /// Picosecond 3: /// 0 1 2 3 4 5 6 /// [ ] [ ] ... (.) [ ] ... [ ] /// [S] [S] [ ] [ ] /// [ ] [ ] [ ] /// [S] [S] /// /// 0 1 2 3 4 5 6 /// [S] [S] ... (.) [ ] ... [ ] /// [ ] [ ] [ ] [ ] /// [ ] [S] [S] /// [ ] [ ] /// /// /// Picosecond 4: /// 0 1 2 3 4 5 6 /// [S] [S] ... ... ( ) ... [ ] /// [ ] [ ] [ ] [ ] /// [ ] [S] [S] /// [ ] [ ] /// /// 0 1 2 3 4 5 6 /// [ ] [ ] ... ... ( ) ... [ ] /// [S] [S] [S] [S] /// [ ] [ ] [ ] /// [ ] [ ] /// /// /// Picosecond 5: /// 0 1 2 3 4 5 6 /// [ ] [ ] ... ... [ ] (.) [ ] /// [S] [S] [S] [S] /// [ ] [ ] [ ] /// [ ] [ ] /// /// 0 1 2 3 4 5 6 /// [ ] [S] ... ... [S] (.) [S] /// [ ] [ ] [ ] [ ] /// [S] [ ] [ ] /// [ ] [ ] /// /// /// Picosecond 6: /// 0 1 2 3 4 5 6 /// [ ] [S] ... ... [S] ... (S) /// [ ] [ ] [ ] [ ] /// [S] [ ] [ ] /// [ ] [ ] /// /// 0 1 2 3 4 5 6 /// [ ] [ ] ... ... [ ] ... ( ) /// [S] [S] [S] [S] /// [ ] [ ] [ ] /// [ ] [ ] /// ``` /// /// In this situation, you are *caught* in layers `0` and `6`, because your /// packet entered the layer when its scanner was at the top when you /// entered it. You are *not* caught in layer `1`, since the scanner moved /// into the top of the layer once you were already there. /// /// The *severity* of getting caught on a layer is equal to its *depth* /// multiplied by its *range*. (Ignore layers in which you do not get /// caught.) The severity of the whole trip is the sum of these values. In /// the example above, the trip severity is `0*3 + 6*4 = 24`. /// /// ``` /// # use advent_solutions::advent2017::day13::part1; /// # let input = "0: 3 /// # 1: 2 /// # 4: 4 /// # 6: 4 /// # "; /// assert_eq!(part1(&input), 24); /// ``` /// /// Given the details of the firewall you've recorded, if you leave /// immediately, *what is the severity of your whole trip*? pub fn part1(input: &str) -> usize { let mut firewall = Firewall::new(&input); let mut severity = 0; for depth in 0..firewall.len() { if let Some(layer) = firewall[depth] { if layer.position == 0 { severity += depth * layer.range; } } firewall.step(); } severity } /// Now, you need to pass through the firewall without being caught - easier /// said than done. /// /// You can't control the <span title="Seriously, what network stack doesn't /// let you adjust the speed of light?">speed of the packet</span>, but you /// can *delay* it any number of picoseconds. For each picosecond you delay /// the packet before beginning your trip, all security scanners move one step. /// You're not in the firewall during this time; you don't enter layer `0` /// until you stop delaying the packet. /// /// In the example above, if you delay `10` picoseconds (picoseconds `0` - /// `9`), you won't get caught: /// /// ```text /// State after delaying: /// 0 1 2 3 4 5 6 /// [ ] [S] ... ... [ ] ... [ ] /// [ ] [ ] [ ] [ ] /// [S] [S] [S] /// [ ] [ ] /// /// Picosecond 10: /// 0 1 2 3 4 5 6 /// ( ) [S] ... ... [ ] ... [ ] /// [ ] [ ] [ ] [ ] /// [S] [S] [S] /// [ ] [ ] /// /// 0 1 2 3 4 5 6 /// ( ) [ ] ... ... [ ] ... [ ] /// [S] [S] [S] [S] /// [ ] [ ] [ ] /// [ ] [ ] /// /// /// Picosecond 11: /// 0 1 2 3 4 5 6 /// [ ] ( ) ... ... [ ] ... [ ] /// [S] [S] [S] [S] /// [ ] [ ] [ ] /// [ ] [ ] /// /// 0 1 2 3 4 5 6 /// [S] (S) ... ... [S] ... [S] /// [ ] [ ] [ ] [ ] /// [ ] [ ] [ ] /// [ ] [ ] /// /// /// Picosecond 12: /// 0 1 2 3 4 5 6 /// [S] [S] (.) ... [S] ... [S] /// [ ] [ ] [ ] [ ] /// [ ] [ ] [ ] /// [ ] [ ] /// /// 0 1 2 3 4 5 6 /// [ ] [ ] (.) ... [ ] ... [ ] /// [S] [S] [S] [S] /// [ ] [ ] [ ] /// [ ] [ ] /// /// /// Picosecond 13: /// 0 1 2 3 4 5 6 /// [ ] [ ] ... (.) [ ] ... [ ] /// [S] [S] [S] [S] /// [ ] [ ] [ ] /// [ ] [ ] /// /// 0 1 2 3 4 5 6 /// [ ] [S] ... (.) [ ] ... [ ] /// [ ] [ ] [ ] [ ] /// [S] [S] [S] /// [ ] [ ] /// /// /// Picosecond 14: /// 0 1 2 3 4 5 6 /// [ ] [S] ... ... ( ) ... [ ] /// [ ] [ ] [ ] [ ] /// [S] [S] [S] /// [ ] [ ] /// /// 0 1 2 3 4 5 6 /// [ ] [ ] ... ... ( ) ... [ ] /// [S] [S] [ ] [ ] /// [ ] [ ] [ ] /// [S] [S] /// /// /// Picosecond 15: /// 0 1 2 3 4 5 6 /// [ ] [ ] ... ... [ ] (.) [ ] /// [S] [S] [ ] [ ] /// [ ] [ ] [ ] /// [S] [S] /// /// 0 1 2 3 4 5 6 /// [S] [S] ... ... [ ] (.) [ ] /// [ ] [ ] [ ] [ ] /// [ ] [S] [S] /// [ ] [ ] /// /// /// Picosecond 16: /// 0 1 2 3 4 5 6 /// [S] [S] ... ... [ ] ... ( ) /// [ ] [ ] [ ] [ ] /// [ ] [S] [S] /// [ ] [ ] /// /// 0 1 2 3 4 5 6 /// [ ] [ ] ... ... [ ] ... ( ) /// [S] [S] [S] [S] /// [ ] [ ] [ ] /// [ ] [ ] /// ``` /// /// Because all smaller delays would get you caught, the fewest number of /// picoseconds you would need to delay to get through safely is `10`. /// /// ``` /// # use advent_solutions::advent2017::day13::part2; /// # let input = "0: 3 /// # 1: 2 /// # 4: 4 /// # 6: 4 /// # "; /// assert_eq!(part2(&input), 10); /// ``` /// /// *What is the fewest number of picoseconds* that you need to delay the /// packet to pass through the firewall without being caught? pub fn part2(input: &str) -> usize { let firewall = Firewall::new(&input); for delay in 0.. { let caught = firewall.0.iter() .enumerate() .any(|(i, layer)| match *layer { Some(Layer { range, .. }) => (delay + i) % (range * 2 - 2) == 0, None => false, }); if !caught { return delay; } } unreachable!(); } pub fn parse_input(input: &str) -> &str { input } test_day!("13", 648, 3933124);