diff --git a/day25.py b/day25.py
new file mode 100644
index 0000000..dc01727
--- /dev/null
+++ b/day25.py
@@ -0,0 +1,120 @@
+from intcode import parse, emulator, REPL
+import re
+
+
+N = 'north'
+S = 'south'
+E = 'east'
+W = 'west'
+
+back = {N : S, S : N, W : E, E : W}
+
+def add_vec(xy, d):
+    x, y = xy
+    if d == N:
+        return (x, y+1)
+    if d == S:
+        return (x, y-1)
+    if d == W:
+        return (x-1, y)
+    if d == E:
+        return (x+1, y)
+
+class Room:
+    def __init__(self, mssg, path):
+        blocks = mssg.strip().split("\n\n")
+        head_str = blocks[0]
+        door_str = blocks[1]
+        item_str = '\n'.join(blocks[2:])
+
+        self.name = re.findall('=+ ([^=]+) =+', head_str)[0]
+        self.description = re.findall(r'=\n([\s\S]+)', head_str)[-1].rstrip()
+        self.doors = re.findall(r'- (\w+)\n?', door_str)
+        self.items = re.findall(r'- (.+)\n?', item_str)
+        self.path = path
+
+    def __eq__(self, other):
+        return self.name == other.name
+
+    def __repr__(self):
+        head = "== {} ==\n{}".format(self.name, self.description)
+        doors = "Doors here lead:\n- {}".format("\n- ".join(self.doors))
+        items = "" if self.items == [] else "\n\nItems here:\n- {}".format("\n- ".join(self.items))
+        path = " -> ".join(self.path)
+        return "{}\n\n{}{}\n{}".format(head, doors, items, path)
+
+
+def encode(s):
+    return map(ord, s + '\n')
+
+def decode(lst):
+    return ''.join(map(chr, lst))
+
+def goto_room(repl, room):
+    for d in room.path:
+        repl.write(d)
+        next(repl)
+
+def try_item(repl, item):
+    if item in ("infinite loop", "giant electromagnet"):
+        return False
+    repl = repl.copy()
+    repl.write("take " + item)
+    next(repl)
+    try:
+        repl.write('')
+        next(repl)
+        return True
+    except StopIteration:
+        return False
+
+def map_ship(repl):
+    rooms = []
+    items = []
+    def aux(path):
+        s = next(repl) 
+        try:
+            room = Room(s, path)
+        except:
+            return
+        if room in rooms:
+           return 
+        rooms.append(room)
+
+        for item in room.items:
+            if not try_item(repl, item):
+                continue
+            repl.write("take " + item) 
+            next(repl)
+            items.append(item)
+
+        for d in room.doors:
+            repl.write(d)
+            aux(path + [d])
+            repl.write(back[d])
+            next(repl)
+    aux([])
+    return rooms, items
+
+def preproc(puzzle_input):
+    prog = parse(puzzle_input)
+    emul = emulator(prog)
+    repl = REPL(emul, decode=decode, encode=encode)
+
+    rooms, items = map_ship(repl)
+
+    checkpoint = list(filter(lambda room : room.name == "Security Checkpoint", rooms))[0]
+    goto_room(repl, checkpoint)
+    return repl
+
+def partI(repl):
+    for item in ["coin", "mutex", "astronaut ice cream", "dehydrated water"]:
+        repl.write("drop " + item)
+        next(repl)
+    repl.write("north")
+    s = next(repl)
+    return re.findall(r'\d+', s)[0]
+
+def partII(_):
+    return "No solution"
+
diff --git a/intcode.py b/intcode.py
index a095547..0513aa4 100644
--- a/intcode.py
+++ b/intcode.py
@@ -44,7 +44,7 @@ class emulator():
         Input is fed from an iterator. This iterator is empty by default. Use
         write/append to add overwrite/append to the input iterator.
         """
-        self.memory = defaultlist(program[:], val_factory = lambda : 0)
+        self.memory = defaultlist(program.copy(), val_factory = lambda : 0)
         self.i = 0 
         self.rel_base = 0
 
@@ -177,6 +177,56 @@ class emulator():
         other.pipe_from(self)
         return other
 
+    @format_input_args
+    def copy(self, input_iter_copy):
+        """
+        Copies emulator instance. The input iterator must be copied and provided
+        by the caller.
+        """
+        new = emulator(self.memory)
+        new.i = self.i
+        new.rel_base = self.rel_base
+
+        new.input_iter = input_iter_copy
+        return new
+
+# Repl class -------------------------------------------------------
+class REPL:
+    """Read-eval-print loop class."""
+    def __init__(self, emul, decode=list, encode=list):
+        """Takes an emulator and decode/enocde functions"""
+        self.emul = emul
+        self.encode = encode
+        self.decode = decode
+
+    def __next__(self):
+        """
+        Iterates over emulator output until WaitForInput is risen or the
+        emulator halts. Returns decoded output.
+        """
+        out = []
+        try:
+            done = True
+            for o in self.emul:
+                done = False
+                out.append(o)
+            if done:
+                raise StopIteration
+        except WaitForInput:
+            pass
+        return self.decode(out)
+
+    def __iter__(self):
+        return self
+
+    def write(self, i):
+        """Encodes input and writes it to emulator"""
+        self.emul.write_input(input_iter = self.encode(i))
+
+    def copy(self):
+        """Copies repl instance."""
+        return REPL(self.emul.copy(), self.decode, self.encode)
+
 # Useful functions --------------------------------------------------
 
 def parse(s):