2015/08-10, 2015/12-13, started on 2015/14

2015/10/Cargo.lock

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+[[package]]
+name = "day-10"
+version = "0.1.0"
+

2015/10/Cargo.toml

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+[package]
+name = "day-10"
+version = "0.1.0"
+authors = ["logaritmisk <anders.e.olsson@gmail.com>"]
+
+[dependencies]

2015/10/input.txt

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+1113122113

2015/10/src/main.rs

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+use std::io::{self, Read};
+use std::iter::Iterator;
+
+
+#[derive(Debug, PartialEq, Clone, Copy)]
+enum Digit {
+    One,
+    Two,
+    Three,
+}
+
+
+struct LookAndSay {
+    values: Vec<Digit>,
+}
+
+impl LookAndSay {
+    fn from_string(input: &str) -> Self {
+        let values = input
+            .chars()
+            .map(|c| match c {
+                '1' => Digit::One,
+                '2' => Digit::Two,
+                '3' => Digit::Three,
+                _ => panic!("invalid input"),
+            })
+            .collect::<Vec<_>>();
+
+        LookAndSay { values: values }
+    }
+}
+
+impl Iterator for LookAndSay {
+    type Item = Vec<Digit>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let mut values = Vec::new();
+
+        let mut state = self.values[0];
+        let mut count = 0;
+
+        for value in &self.values {
+            if *value == state {
+                count += 1;
+            } else {
+                values.push(match count {
+                    1 => Digit::One,
+                    2 => Digit::Two,
+                    3 => Digit::Three,
+                    _ => unreachable!(),
+                });
+
+                values.push(state);
+
+                state = *value;
+                count = 1;
+            }
+        }
+
+        values.push(match count {
+            1 => Digit::One,
+            2 => Digit::Two,
+            3 => Digit::Three,
+            _ => unreachable!(),
+        });
+
+        values.push(state);
+
+        self.values = values.clone();
+
+        Some(values)
+    }
+}
+
+
+fn main() {
+    let mut input = String::new();
+
+    io::stdin()
+        .read_to_string(&mut input)
+        .expect("faild to read input");
+
+    for line in input
+        .lines()
+        .map(|line| line.trim())
+        .filter(|line| !line.is_empty())
+    {
+        let mut look_and_say = LookAndSay::from_string(line);
+
+        // Skip 39 iterations to get number 40.
+        if let Some(value) = look_and_say.nth(39) {
+            println!("part_one={}", value.len());
+        }
+
+        // Skip 9 more iterations to get number 50.
+        if let Some(value) = look_and_say.nth(9) {
+            println!("part_two={}", value.len());
+        }
+    }
+}