Implement day 08 in rust.

2018/src/day08.rs

@@ -0,0 +1,100 @@
+use std::io::Read;
+
+use common::Solution;
+
+#[derive(Default)]
+pub struct Day08 {}
+
+
+fn total1(items: &[usize]) -> (usize, usize) {
+    let children = items[0];
+    let meta_entries = items[1];
+
+    let mut total = 0;
+    let mut start = 2;
+
+    for _ in 0..children {
+        let (ct, cl) = total1(&items[start..items.len()]);
+        start += cl;
+        total += ct;
+    }
+
+    total += items[start..(start + meta_entries)].iter().sum::<usize>();
+
+    (total, start + meta_entries)
+}
+
+fn total2(items: &[usize]) -> (usize, usize) {
+    let children = items[0];
+    let meta_entries = items[1];
+
+    if children == 0 {
+        (items[2..(2 + meta_entries)].iter().sum(), meta_entries + 2)
+    } else {
+        let mut values = Vec::with_capacity(children);
+
+        let mut start = 2;
+
+        for _ in 0..children {
+            let (ct, cl) = total2(&items[start..items.len()]);
+            start += cl;
+            values.push(ct);
+        }
+
+        let total = items[start..(start + meta_entries)].iter()
+            .filter(|&&x| x <= values.len())
+            .map(|&x| values[x - 1])
+            .sum();
+
+        (total, start + meta_entries)
+    }
+}
+
+
+impl Day08 {
+    pub fn new() -> Self {
+        Default::default()
+    }
+}
+
+impl Solution for Day08 {
+    fn part1(&mut self, input: &mut Read) -> String {
+        let mut data = String::new();
+        input.read_to_string(&mut data).unwrap();
+
+        let data: Vec<usize> = data.trim().split(" ").map(|x| x.parse().unwrap()).collect();
+        let (result, _) = total1(&data);
+
+        format!("{}", result)
+    }
+
+    fn part2(&mut self, input: &mut Read) -> String {
+        let mut data = String::new();
+        input.read_to_string(&mut data).unwrap();
+
+        let data: Vec<usize> = data.trim().split(" ").map(|x| x.parse().unwrap()).collect();
+        let (result, _) = total2(&data);
+
+        format!("{}", result)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use common::Solution;
+    use day08::Day08;
+
+    const SAMPLE_INPUT: &[u8] = include_bytes!("samples/08.txt");
+
+    #[test]
+    fn sample_part1() {
+        let mut instance = Day08::new();
+        assert_eq!("138", instance.part1(&mut SAMPLE_INPUT));
+    }
+
+    #[test]
+    fn sample_part2() {
+        let mut instance = Day08::new();
+        assert_eq!("66", instance.part2(&mut SAMPLE_INPUT));
+    }
+}

2018/src/samples/08.txt

@@ -0,0 +1 @@
+2 3 0 3 10 11 12 1 1 0 1 99 2 1 1 2