diff --git a/day02.py b/day02.py
index ca86131..1a5ce05 100644
--- a/day02.py
+++ b/day02.py
@@ -1,4 +1,3 @@
-from lib import format_main
 from itertools import product
 from operator import mul, add
 
diff --git a/day07.py b/day07.py
index b823eff..a0ca7ca 100644
--- a/day07.py
+++ b/day07.py
@@ -1,5 +1,4 @@
-from lib import format_main
-from intcode import Interpreter, makeIO, Singleton
+from intcode import Interpreter, makeIO, Singleton, Halted
 from itertools import permutations
 
 stack_size = 5
@@ -32,16 +31,14 @@ def partII(amp):
     for perm in permutations(phase_range):
         amps = [amp() for _ in range(stack_size)]
         for p, a in zip(perm, amps):
-            a.write([p])
-            next(a)
+            a.eval([p])
 
         amp_in = fst_amp_input
         while True:
             try:
                 for a in amps:
-                    a.write([amp_in])
-                    amp_in = next(a)
-            except StopIteration:
+                    amp_in = a.eval([amp_in])
+            except Halted:
                 break
         best = max(amp_in, best)
     
diff --git a/intcode.py b/intcode.py
index a6cda49..e59299c 100644
--- a/intcode.py
+++ b/intcode.py
@@ -1,16 +1,13 @@
-from collections import defaultdict
+from collections import defaultdict, deque
 from enum import Enum
 from inspect import signature
 import operator
 
-class IntcodeError(Exception):
+class WaitForInput(Exception):
     pass
 
-class OpState(Enum):
-    """Execution state class."""
-    CONTINUE = 0
-    HALT     = 1
-    WAIT     = 2
+class Halted(Exception):
+    pass
 
 class defaultlist(list):
     """Default list class. Allows writing and reading out of bounds."""
@@ -28,6 +25,89 @@ class defaultlist(list):
             return self.val_factory() 
         return super().__getitem__(i)
 
+
+class Emulator(object):
+    def __init__(self, program, get_input, put_output):
+        self.in_f = get_input
+        self.out_f = put_output
+        
+        self.memory = defaultlist(program[:], val_factory = lambda : 0)
+        self.i = 0 
+        self.rel_base = 0
+
+    def _of_operator(operator):
+        """Make opcode from operator."""
+        def opcode(self, p1, p2, p3):
+            r = operator(self.memory[p1], self.memory[p2])
+            self.memory[p3] = r
+            self.i += 4
+        return opcode 
+
+    def _jump_when(flag):
+        def opcode(self, p1, p2):
+            if (self.memory[p1] > 0) == flag:
+                self.i = self.memory[p2]
+            else:
+                self.i += 3
+        return opcode 
+
+    def _get_input(self, p1):
+        x = self.in_f()
+        self.memory[p1] = x
+        self.i += 2
+
+    def _put_output(self, p1):
+        self.i += 2
+        self.out_f(self.memory[p1])
+
+    def _adjust_base(self, p1):
+        self.rel_base += self.memory[p1]
+        self.i += 2
+ 
+    opcodes = {1  : _of_operator(operator.add),
+               2  : _of_operator(operator.mul),
+               3  : _get_input,
+               4  : _put_output,
+               5  : _jump_when(True), 
+               6  : _jump_when(False),
+               7  : _of_operator(operator.lt),
+               8  : _of_operator(operator.eq),
+               9  : _adjust_base,
+              }
+
+    def __next__(self):
+        state = self
+        op = str(self.memory[state.i])
+
+        if op == '99':
+            raise StopIteration
+
+        par_modes, op = op[:-2][::-1], int(op[-2:])
+
+        opcode = self.opcodes[op]
+        parnum = len(signature(opcode).parameters) - 1
+        par_modes = par_modes + '0'*(parnum - len(par_modes))
+        par_modes = map(int, par_modes)
+
+        pars = []
+        for pn, mode in enumerate(par_modes, start=1):
+            p = state.i + pn
+            if mode == 0:
+                p = state.memory[p]
+            elif mode == 2:
+                p = state.rel_base + state.memory[p]
+            pars.append(p)
+        opcode(state, *pars)
+
+    def __iter__(self):
+        return self
+
+    def run(self):
+        if self.memory[self.i] == 99:
+            raise Halted
+        return deque(self, maxlen=0)
+
+
 class Singleton(object):
     def __init__(self, x=None):
         self.x = x
@@ -64,7 +144,7 @@ def makeIO(in_buff_class, out_buff_class):
 
         def pop_input(self):
             if self.in_buff == in_buff_class(): 
-                return None
+                raise WaitForInput
             return self.in_buff.pop(0)
 
         def append_output(self, x):
@@ -94,98 +174,21 @@ def makeIO(in_buff_class, out_buff_class):
 StackIO = makeIO(list, list)
 SingletonIO = makeIO(Singleton, Singleton)
 
-class Opcode:
-    def of_operator(operator):
-        """Make opcode from operator."""
-        def opcode(state, p1, p2, p3):
-            r = operator(state.memory[p1], state.memory[p2])
-            state.memory[p3] = r
-            state.i += 4
-            return OpState.CONTINUE
-        return opcode 
-
-    def jump_when(flag):
-        def opcode(state, p1, p2):
-            if (state.memory[p1] > 0) == flag:
-                state.i = state.memory[p2]
-            else:
-                state.i += 3
-            return OpState.CONTINUE
-        return opcode 
-
-    def adjust_base(state, p1):
-        state.rel_base += state.memory[p1]
-        state.i += 2
-        return OpState.CONTINUE
-
-    def get_input(state, p1):
-        x = state.IO.pop_input()
-        if x == None:
-            return OpState.WAIT
-        state.memory[p1] = x
-        state.i += 2
-        return OpState.CONTINUE
-
-    def put_output(state, p1):
-        state.IO.append_output(state.memory[p1])
-        state.i += 2
-        return OpState.CONTINUE
-
-    halt = lambda _ : OpState.HALT
-
-    ops = {1  : of_operator(operator.add),
-           2  : of_operator(operator.mul),
-           3  : get_input,
-           4  : put_output,
-           5  : jump_when(True), 
-           6  : jump_when(False),
-           7  : of_operator(operator.lt),
-           8  : of_operator(operator.eq),
-           9  : adjust_base,
-           99 : halt
-          }
-
-    def parse(op):
-        op = str(op)
-        par_modes, op = op[:-2][::-1], int(op[-2:])
-
-        opcode = Opcode.ops[op]
-        parnum = len(signature(opcode).parameters) - 1
-        par_modes = par_modes + '0'*(parnum - len(par_modes))
-
-        return opcode, map(int, par_modes)
-
-    def run(state):
-        opcode, par_modes = Opcode.parse(state.memory[state.i])
-        pars = []
-        for pn, mode in enumerate(par_modes, start=1):
-            p = state.i + pn
-            if mode == 0:
-                p = state.memory[p]
-            elif mode == 2:
-                p = state.rel_base + state.memory[p]
-            pars.append(p)
-        op_state = opcode(state, *pars)
-        return op_state
-
 
 
 class Interpreter(object):
-    def __init__(self, program, IO_class=StackIO, i=0, rel_base=0):
-        self.memory = defaultlist(program[:], val_factory = lambda : 0)
+    def __init__(self, program, IO_class=StackIO):
         self.IO = IO_class()
-        self.i = i
-        self.rel_base = rel_base
+        self.comp = Emulator(program, self.IO.pop_input, self.IO.append_output)
 
     def __iter__(self):
-        return self
-  
-    def __next__(self):
-        if Opcode.run(self) == OpState.HALT:
-            raise StopIteration
-        while Opcode.run(self) == OpState.CONTINUE:
-            continue
-        return self.IO.flush()
+        while True:
+            try:
+                self.comp.run()
+                break
+            except WaitForInput: 
+                yield self.IO.flush()
+        yield self.IO.flush()
 
     def write(self, in_buff):
         self.IO.write(in_buff) 
@@ -193,10 +196,17 @@ class Interpreter(object):
     def run(self, in_buff=None):
         if in_buff != None:
             self.write(in_buff)
-        out = next(self)
-        if Opcode.run(self) != OpState.HALT:
-            raise IntcodeError("expecting input")
-        return out
+        self.comp.run()
+        return self.IO.flush()
+
+    def eval(self, in_buff):
+        self.write(in_buff)
+        try:
+            self.comp.run()
+        except WaitForInput:
+            pass
+        return self.IO.flush()
+
 
     def copy(self):
         memory = self.memory.copy()
diff --git a/lib.py b/lib.py
new file mode 100644
index 0000000..18d77c2
--- /dev/null
+++ b/lib.py
@@ -0,0 +1,83 @@
+
+class Graph(dict):
+    nodes = dict.keys
+
+    def add_node(self, a):
+        if a not in self:
+            self[a] = []
+
+    def add_edge(self, a, b):
+        self.add_node(a)
+        self.add_node(b)
+        self[a].append(b)
+        self[b].append(a)
+
+    def nodes_of(self, a):
+        return self[a]
+
+    def rm_loops(self):
+        for a in self.keys():
+            for i, b in enumerate(self.nodes_of(a)):
+                if a == b:
+                    del self[a][i]
+
+    def min_path(self, a, b):
+        weights = dict() 
+        visited = set()
+
+        node, w = a, 0
+        while node != b:
+            for c in self[node]:
+                if c in visited:
+                    continue
+                if c in weights and weights[c] <= w + 1:
+                    continue
+                weights[c] = w + 1 
+            node, w = min(weights.items() , key=lambda x: x[1])
+            del weights[node]
+            visited.add(node)
+        return w
+
+    def min_paths(self, a):
+        weights = dict() 
+        visited = set()
+        visited.add(a)
+
+        node, w = a, 0
+        while len(visited) != len(self):
+            for c in self[node]:
+                if c in visited:
+                    continue
+                if c in weights and weights[c] <= w + 1:
+                    continue
+                weights[c] = w + 1 
+            node, w = min(filter(lambda x: x[0] not in visited, weights.items()) , key=lambda x: x[1])
+            visited.add(node)
+        return weights 
+
+
+
+class WeightedGraph(Graph):
+    def nodes_of(self, a):
+        return [b for b, _ in self[a]]
+
+    def add_edge(self, a, b, w):
+        self[a].append((b, w))
+        self[b].append((a, w))
+
+    def min_path(self, a, b):
+        weights = dict() 
+        visited = set()
+
+        node, w = a, 0
+        while node != b:
+            for c, edge_w in self[node]:
+                if c in visited:
+                    continue
+                if c in weights and weights[c] <= w + edge_w:
+                    continue
+                weights[c] = w + edge_w
+            node, w = min(weights.items() , key=lambda x: x[1])
+            del weights[node]
+            visited.add(node)
+        return w