diff --git a/src/bin/04.rs b/src/bin/04.rs
new file mode 100644
index 0000000000..36dbaa9
--- /dev/null
+++ b/src/bin/04.rs
@@ -0,0 +1,98 @@
+use hashbrown::HashMap;
+use itertools::Itertools;
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let mut res = 0;
+
+    for room in input.lines() {
+        if let Some((checksum, code)) = room.split('-').collect_vec().split_last() {
+            let mut letters = HashMap::new();
+
+            for word in code.iter() {
+                for letter in word.chars() {
+                    *letters.entry(letter).or_insert(0) += 1;
+                }
+            }
+
+            let checksum = checksum.replace(']', "").to_string();
+
+            let (id, order) = checksum.split_once('[').unwrap();
+            let code = letters
+                .into_iter()
+                .sorted_by(|kv1, kv2| kv2.1.cmp(&kv1.1).then_with(|| kv1.0.cmp(&kv2.0)))
+                .take(5)
+                .map(|(k, _)| k)
+                .collect::<String>();
+
+            if order == code {
+                res += id.parse::<u32>().unwrap();
+            }
+        }
+    }
+
+    Some(res)
+}
+pub fn part_two(input: &str) -> Option<usize> {
+    for room in input.lines() {
+        if let Some((checksum, codes)) = room.split('-').collect_vec().split_last() {
+            let mut letters = HashMap::new();
+
+            for word in codes.iter() {
+                for letter in word.chars() {
+                    *letters.entry(letter).or_insert(0) += 1;
+                }
+            }
+
+            let checksum = checksum.replace(']', "").to_string();
+
+            let (id, order) = checksum.split_once('[').unwrap();
+            let id = id.parse().unwrap();
+
+            let code = letters
+                .into_iter()
+                .sorted_by(|kv1, kv2| kv2.1.cmp(&kv1.1).then_with(|| kv1.0.cmp(&kv2.0)))
+                .take(5)
+                .map(|(k, _)| k)
+                .collect::<String>();
+
+            if order == code {
+                let decrypted = codes
+                    .iter()
+                    .map(|x| {
+                        x.chars()
+                            .map(|x| {
+                                let index = ('a'..='z').position(|y| y == x).unwrap();
+                                ('a'..='z').cycle().nth(index + id).unwrap()
+                            })
+                            .collect::<String>()
+                    })
+                    .collect_vec()
+                    .join(" ");
+                if decrypted == "northpole object storage" {
+                    return Some(id);
+                }
+            }
+        }
+    }
+
+    None
+}
+fn main() {
+    let input = &aoc::read_file("inputs", 4);
+    aoc::solve!(1, part_one, input);
+    aoc::solve!(2, part_two, input);
+}
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        let input = aoc::read_file("examples", 4);
+        assert_eq!(part_one(&input), Some(1514));
+    }
+    #[test]
+    fn test_part_two() {
+        let input = aoc::read_file("examples", 4);
+        assert_eq!(part_two(&input), None);
+    }
+}
diff --git a/src/examples/04.txt b/src/examples/04.txt
new file mode 100644
index 0000000000..1d296af
--- /dev/null
+++ b/src/examples/04.txt
@@ -0,0 +1,4 @@
+aaaaa-bbb-z-y-x-123[abxyz]
+a-b-c-d-e-f-g-h-987[abcde]
+not-a-real-room-404[oarel]
+totally-real-room-200[decoy]