diff --git a/12/12.py b/12/12.py
new file mode 100644
index 0000000..b67ddb2
--- /dev/null
+++ b/12/12.py
@@ -0,0 +1,89 @@
+from collections import defaultdict
+d4 = [(-1, 0), (0, 1), (1, 0), (0, -1)]
+
+
+
+def make_field(data):
+    data = data.strip().split("\n")
+    data = ['.'*len(data[0])] + data + ['.'*len(data[0])]
+    data = ['.'+x+'.' for x in data]
+    return data
+
+def regions(data, collect=len):
+    def walk(i, j, c):
+        nonlocal borders
+        if data[i][j]!=c:
+            return
+        if (i, j) not in region:
+            region.add((i, j))
+            for di, dj in d4:
+                if (i+di, j+dj) not in region:
+                    borders += 1
+                else:
+                    borders -= 1
+            for di, dj in d4:
+                walk(i+di, j+dj, c)
+    unmarked = {(i, j) for i in range(1, len(data)-1) for j in range(1, len(data)-1)}
+    regions = []
+    while unmarked:
+        i, j = next(iter(unmarked))
+        region = set()
+        borders = 0
+        walk(i, j, data[i][j])
+        regions.append((collect(region), borders))
+        unmarked -= region
+    return regions
+
+def sides(data):        
+    for region, _ in regions(data, collect=lambda x: x):
+        net = defaultdict(lambda: [0,0,0,0])
+        for i, j in region:
+            net[(i, j)][3] = 1
+            net[(i+1, j)][0] = 1
+            net[(i, j+1)][2] = 1
+            net[(i+1, j+1)][1] = 1
+        net2 = defaultdict(list)
+        for (i, j), (a,b,c,d) in net.items():
+            if a!=d:
+                net2[(i, j)].append((i, j+1))
+            if a!=b:
+                net2[(i, j)].append((i-1, j))
+            if b!=c:
+                net2[(i, j)].append((i, j-1))
+            if c!=d:
+                net2[(i, j)].append((i+1, j))
+        borders = 0
+        while net2:
+            s = min(net2)
+            p = s
+            n = net2[s][0]
+            net2[s].remove(n)
+            
+            borders += 1
+            while not n==s:
+                pi, pj = p
+                ni, nj = n
+                net2[n].remove(p)
+                if len(net2[n])!=1:
+                    a = (ni + nj-pj, nj + ni-pi)
+                else:
+                    a = (ai, aj) = net2[n][0]
+                net2[n].remove(a)
+                if len(net2[n])==0:
+                    del net2[n]
+                if not((abs(ni-pi)==abs(ai-ni)==1) or (abs(nj-pj)==abs(aj-nj)==1)):
+                    borders += 1
+                p = n
+                n = a
+            del net2[n]
+        yield len(region), borders
+                
+                
+data = open("input.txt").read()
+
+print(sum(a*b for a, b in regions(make_field(data))))
+
+print(sum(a*b for a, b in sides(make_field(data))))
+
+import cProfile
+cProfile.run('sum(a*b for a, b in sides(make_field(data)))')