2018/05

2018/05/Cargo.lock

@@ -0,0 +1,4 @@
+[[package]]
+name = "day-05"
+version = "0.1.0"
+

2018/05/example-01.txt

@@ -0,0 +1 @@
+dabAcCaCBAcCcaDA

2018/05/src/main.rs

@@ -1,3 +1,88 @@
-fn main() {
-    println!("Hello, world!");
+use std::collections::HashSet;
+use std::io::{self, BufRead};
+
+fn react<I>(polymer: I) -> String
+where
+    I: Iterator<Item = char>,
+{
+    let mut input = polymer.collect::<Vec<char>>();
+
+    loop {
+        let remove = input
+            .windows(2)
+            .enumerate()
+            .filter(|(_, chars)| {
+                assert!(chars.len() == 2);
+
+                let left = chars[0];
+                let right = if chars[1].is_uppercase() {
+                    chars[1].to_ascii_lowercase()
+                } else {
+                    chars[1].to_ascii_uppercase()
+                };
+
+                left == right
+            })
+            .map(|(i, _)| i)
+            .scan(None, |state, i| {
+                if let Some(n) = state {
+                    let prev = *n + 1;
+
+                    *n = i;
+
+                    if prev != i {
+                        Some(i)
+                    } else {
+                        None
+                    }
+                } else {
+                    *state = Some(i);
+
+                    Some(i)
+                }
+            })
+            .collect::<Vec<_>>();
+
+        if remove.is_empty() {
+            break;
+        }
+
+        input = input
+            .into_iter()
+            .enumerate()
+            .filter(|(i, _)| !remove.contains(i) && !remove.contains(&(i - 1)))
+            .map(|(_, c)| c)
+            .collect::<Vec<_>>();
+    }
+
+    input.into_iter().collect::<String>()
+}
+
+fn main() {
+    let input = io::stdin()
+        .lock()
+        .lines()
+        .filter_map(Result::ok)
+        .collect::<String>();
+
+    println!("part.one={}", react(input.chars()).len());
+
+    let units = input
+        .chars()
+        .map(|c| c.to_ascii_lowercase())
+        .collect::<HashSet<_>>();
+
+    let min = units
+        .into_iter()
+        .map(|u| {
+            let stream = input
+                .chars()
+                .filter(|c| *c != u && *c != u.to_ascii_uppercase());
+
+            react(stream).len()
+        })
+        .min()
+        .expect("failed to find shortest polymer");
+
+    println!("part.two={}", min);
 }