1 files changed, 83 insertions, 0 deletions
diff --git a/2016/aoc4/src/main.rs b/2016/aoc4/src/main.rs
new file mode 100644
index 0000000..ea1edd8
--- /dev/null
+++ b/2016/aoc4/src/main.rs
@@ -0,0 +1,83 @@
+use std::io::BufReader;
+use std::io::prelude::*;
+use std::fs::File;
+use std::collections::BTreeMap;
+
+#[derive(Debug)]
+struct Room {
+    encrypted_name: String,
+    sector_id: u32,
+    checksum: String
+}
+
+impl Room {
+    fn new(line: String) -> Room {
+        let name_length = line.find(char::is_numeric).unwrap();
+        let (name, sector_and_check) = line.split_at(name_length);
+        let (sector, check) = sector_and_check.split_at(sector_and_check.len()-7);
+        
+        Room {
+            encrypted_name: name.trim_matches('-').to_string(),
+            sector_id: sector.parse().unwrap(),
+            checksum: check.trim_matches(|c| c=='[' || c==']').to_string()
+        }
+    }
+
+    fn is_valid(&self) -> bool {
+        let mut char_counts: BTreeMap<char, i32> = BTreeMap::new();
+        let chars = self.encrypted_name.chars()
+            .filter(|&c| c != '-');
+        for c in chars {
+            *char_counts.entry(c).or_insert(0) += 1;
+        }
+
+        let mut vec_char_counts = char_counts.iter().collect::<Vec<_>>();
+        vec_char_counts.sort_by_key(|&(_, &value)| -value);
+        let expected_checksum = vec_char_counts
+            .iter()
+            .take(5)
+            .map(|&(&key, _)| key)
+            .collect::<String>();
+
+        expected_checksum == self.checksum
+    }
+
+    fn decrypt_name(&self) -> String {
+        self.encrypted_name.chars().map(|c| {
+            if c == '-' {
+                ' '
+            } else {
+                let current_digit = c as u8 - 'a' as u8;
+                let new_digit = ((current_digit as u32 + self.sector_id) % 26) as u8;
+                (new_digit + 'a' as u8) as char
+            }
+        }).collect()
+    }
+}
+
+fn main() {
+    let rooms = read_file();
+    let valid_rooms = rooms.iter()
+        .filter(|r| r.is_valid())
+        .collect::<Vec<_>>();
+    let sector_sum: u32 = valid_rooms.iter()
+        .map(|r| r.sector_id)
+        .sum();
+
+    println!("Sector sum {}", sector_sum);
+
+    let north_poles = rooms.iter()
+        .filter(|r| r.decrypt_name().contains("north"))
+        .inspect(|r| println!("{} {}", r.decrypt_name(), r.sector_id))
+        .collect::<Vec<_>>();
+    println!("{:?}", north_poles);
+}
+
+fn read_file() -> Vec<Room> {
+    let file = BufReader::new(File::open("input.txt").unwrap());
+    file.lines()
+        .map(|line| line.unwrap().trim().to_string())
+        .filter(|line| line.len() > 0)
+        .map(Room::new)
+        .collect()
+}