diff --git a/src/days.rs b/src/days.rs
index 1c4b09e..bae5f25 100644
--- a/src/days.rs
+++ b/src/days.rs
@@ -9,7 +9,7 @@ pub mod d8;
 pub mod d9;
 pub mod d10;
 pub mod d11;
-// pub mod d12;
+pub mod d12;
 // pub mod d13;
 // pub mod d14;
 // pub mod d15;
diff --git a/src/days/d12.rs b/src/days/d12.rs
new file mode 100644
index 0000000..c1c303c
--- /dev/null
+++ b/src/days/d12.rs
@@ -0,0 +1,121 @@
+use crate::prelude::*;
+
+pub type I = Vec<Inst>;
+pub type O = i64;
+
+pub enum Val {
+    Register (char),
+    Literal (i64),
+}
+
+
+#[allow(dead_code)]
+impl Val {
+    fn new (i: &str) -> Self {
+        match i.parse::<i64>() {
+            Ok(s) => Self::Literal(s),
+            Err(_) => Self::Register(i.chars().next().unwrap())
+        }
+    }
+}
+
+pub enum Inst {
+    Jnz (Val, isize),
+    Cpy (Val, char),
+    Inc (char),
+    Dec (char)
+}
+
+
+
+fn _parse (data: &str) -> I {
+    data.trim().lines().map(|line| {
+        let mut split = line.split_ascii_whitespace();
+        match split.next().unwrap() {
+            "jnz" => {
+                Inst::Jnz(Val::new(split.next().unwrap()), split.next().unwrap().parse().unwrap())
+            },
+            "cpy" => {
+                Inst::Cpy(Val::new(split.next().unwrap()), split.next().unwrap().chars().next().unwrap())
+            },
+            "inc" => {
+                Inst::Inc(split.next().unwrap().chars().next().unwrap())
+            },
+            "dec" => {
+                Inst::Dec(split.next().unwrap().chars().next().unwrap())
+            },
+            _ => unreachable!()
+        }
+    }).collect()
+}
+
+fn _solve (data: I, r: &mut M<char, i64>) {
+    let mut ptr = 0;
+
+    while ptr < data.len() {
+        let i = &data[ptr];
+
+        match i {
+            Inst::Inc(reg) => *r.entry(*reg).or_default() += 1,
+            Inst::Dec(reg) => *r.entry(*reg).or_default() -= 1,
+            Inst::Cpy(val, reg) => {
+                match val {
+                    Val::Literal(val) => *r.entry(*reg).or_default() = *val,
+                    Val::Register(r2) => *r.entry(*reg).or_default() = *r.get(r2).unwrap(),
+                }
+            },
+            Inst::Jnz(val, dest) => {
+                let val = match val {
+                    Val::Literal(val) => *val,
+                    Val::Register(r2) => *r.get(r2).unwrap(),
+                };
+
+                if val != 0 {
+                    ptr = ptr.checked_add_signed(*dest).unwrap_or(0);
+                    continue;
+                }
+
+            }
+
+        }
+        ptr += 1;
+    }
+}
+
+fn _silver (data: I) -> O {
+    let mut state = M::from([('a', 0), ('b', 0), ('c', 0), ('d', 0)]);
+    _solve(data, &mut state);
+    *state.get(&'a').unwrap()
+}
+
+fn _gold (data: I) -> O {
+    let mut state = M::from([('a', 0), ('b', 0), ('c', 1), ('d', 0)]);
+    _solve(data, &mut state);
+    *state.get(&'a').unwrap()
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    fn read () -> I {
+        let data = inc!(12);
+        _parse(data)
+    }
+
+    #[test]
+    fn silver () {
+        let data = read();
+        let ans = _silver(data);
+
+        assert_eq!(ans, 318007)
+    }
+
+    #[test]
+    fn gold () {
+        let data = read();
+        let ans = _gold(data);
+
+        assert_eq!(ans, 9227661)
+    }
+}