Day 8

2 files changed, 69 insertions, 1 deletions

diff --git a/2018/src/day8.rs b/2018/src/day8.rs
new file mode 100644
index 0000000..81f0d0b
--- /dev/null
+++ b/2018/src/day8.rs
@@ -0,0 +1,66 @@
+use std::io;
+use std::io::BufRead;
+
+pub fn main<T: BufRead>(reader: T) -> io::Result<(String, String)> {
+    #[derive(PartialEq, Eq)]
+    struct Entry {
+        nch: i32,
+        nmeta: i32,
+    }
+
+    let mut stk = vec![Entry {nch: 1, nmeta: 0}];
+    let mut total_meta = 0;
+    let mut vals: Vec<Vec<i32>> = vec![vec![]];
+    let mut current_val = 0;
+
+    for num in reader.lines().next().unwrap().unwrap().split(' ').map(|s| s.parse::<i32>().unwrap()) {
+        // Yay non-lexical lifetimes!
+        let l = stk.last_mut().unwrap();
+        if l.nmeta == -1 {
+            // println!("read nmeta {}", num);
+            l.nmeta = num;
+            continue;
+        }
+
+        if l.nmeta == 0 && l.nch == 0 {
+            loop {
+                // println!("pop");
+                stk.pop();
+
+                // println!("  node value {}", current_val);
+                vals.pop();
+                vals.last_mut().unwrap().push(current_val);
+                current_val = 0;
+
+                let l = stk.last().unwrap();
+                if l.nmeta != 0 || l.nch != 0 { break; }
+            }
+        }
+
+        let l = stk.last_mut().unwrap();
+        if l.nch == 0 {
+            // println!("+meta {}", num);
+            total_meta += num;
+
+            if vals.last().unwrap().len() == 0 {
+                // println!("  add value");
+                current_val += num;
+            } else if 1 <= num && num <= vals.last().unwrap().len() as i32 {
+                // println!("  add child value {}", vals.last().unwrap()[num as usize - 1]);
+                current_val += vals.last().unwrap()[num as usize - 1];
+            }
+
+            l.nmeta -= 1;
+        } else {
+            // println!("read nch {}", num);
+            l.nch -= 1;
+            stk.push(Entry {nch: num, nmeta: -1});
+            vals.push(vec![]);
+        }
+    }
+
+    let part1 = total_meta.to_string();
+    let part2 = current_val.to_string();
+
+    Ok((part1, part2))
+}
diff --git a/2018/src/main.rs b/2018/src/main.rs
index fccb319..8d2f368 100644
--- a/2018/src/main.rs
+++ b/2018/src/main.rs
@@ -16,8 +16,9 @@ mod day4;
 mod day5;
 mod day6;
 mod day7;
+mod day8;
 
-static NUM_DAYS: i32 = 7;
+static NUM_DAYS: i32 = 8;
 
 fn day_switch<T: BufRead>(day: i32, reader: T) -> io::Result<(String, String)> {
     match day {
@@ -28,6 +29,7 @@ fn day_switch<T: BufRead>(day: i32, reader: T) -> io::Result<(String, String)> {
         5 => day5::main(reader),
         6 => day6::main(reader),
         7 => day7::main(reader),
+        8 => day8::main(reader),
         _ => Err(Error::new(ErrorKind::Other, "Invalid day"))
     }
 }