Implement day 05.

This was a nice exercise in not allocating memory. Or at least it was,
for part 1.

2018/src/day05.rs

@@ -0,0 +1,68 @@
+use std::io::Read;
+
+use common;
+
+#[derive(Default)]
+pub struct Day05 {}
+
+impl Day05 {
+    pub fn new() -> Day05 {
+        Default::default()
+    }
+
+    fn reduce(mut data: Vec<u8>) -> usize {
+        let mut dptr = 0;
+        for iptr in 0..data.len() {
+            if dptr > 0 && (data[iptr].eq_ignore_ascii_case(&data[dptr - 1])) && data[iptr] != data[dptr - 1] {
+                dptr -= 1;
+            } else {
+                data[dptr] = data[iptr];
+                dptr += 1;
+            }
+        }
+
+        dptr
+    }
+}
+
+impl common::Solution for Day05 {
+    fn part1(&mut self, input: &mut Read) -> String {
+        let mut data = Vec::new();
+        input.read_to_end(&mut data).expect("Can't read input!");
+        common::trim_back(&mut data);
+
+        format!("{}", Day05::reduce(data))
+    }
+
+    fn part2(&mut self, input: &mut Read) -> String {
+        let mut data = Vec::new();
+        input.read_to_end(&mut data).expect("Can't read input!");
+        common::trim_back(&mut data);
+
+        let min_len = (b'a'..=b'z').map(|option| data.iter().filter(|&x| !x.eq_ignore_ascii_case(&option)).map(|&x| x).collect())
+            .map(|x| Day05::reduce(x))
+            .min().unwrap();
+
+        format!("{}", min_len)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use common::Solution;
+    use day05::Day05;
+
+    const SAMPLE_INPUT: &[u8] = b"dabAcCaCBAcCcaDA\n";
+
+    #[test]
+    fn sample_part1() {
+        let mut instance = Day05::new();
+        assert_eq!("10", instance.part1(&mut SAMPLE_INPUT));
+    }
+
+    #[test]
+    fn sample_part2() {
+        let mut instance = Day05::new();
+        assert_eq!("4", instance.part2(&mut SAMPLE_INPUT));
+    }
+}