diff --git a/inputs/18_example.txt b/inputs/18_example.txt
new file mode 100644
index 0000000..fc7612e
--- /dev/null
+++ b/inputs/18_example.txt
@@ -0,0 +1,14 @@
+R 6 (#70c710)
+D 5 (#0dc571)
+L 2 (#5713f0)
+D 2 (#d2c081)
+R 2 (#59c680)
+D 2 (#411b91)
+L 5 (#8ceee2)
+U 2 (#caa173)
+L 1 (#1b58a2)
+U 2 (#caa171)
+R 2 (#7807d2)
+U 3 (#a77fa3)
+L 2 (#015232)
+U 2 (#7a21e3)
diff --git a/solutions/18_example.txt b/solutions/18_example.txt
new file mode 100644
index 0000000..a0f8f97
--- /dev/null
+++ b/solutions/18_example.txt
@@ -0,0 +1,2 @@
+62
+952408144115
diff --git a/src/python/10_rk.py b/src/python/10_rk.py
index c019f66..f681d95 100644
--- a/src/python/10_rk.py
+++ b/src/python/10_rk.py
@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 import sys
 import collections
+import util
 
 """
 assuming there is loop
@@ -150,37 +151,8 @@ def sol1(IN):
             continue
         m[IN[1][0]][IN[1][1]] = c
             
+    ninside = util.calculate_inside(l_loop, m)
 
-    ninside = 0
-    for x, line in enumerate(l_loop):
-        boundary_start = ""
-        inside = False
-        #  print(line)
-        for y, boundary in enumerate(line):
-            if boundary:
-                t = m[x][y]
-                #  print(t)
-                if t == "|":
-                    #  print("flip")
-                    inside = not inside
-                elif boundary_start == "":
-                    #  print("start with ", t)
-                    # this can't be '-'
-                    boundary_start = t
-                elif t != "-":
-                    # skip over -
-                    #  print("end in", t)
-                    #  print(f"{boundary_start}{t}")
-                    if f"{boundary_start}{t}" in ["FJ", "L7"]:
-                        #  print("flip")
-                        # flip only in those cases
-                        inside = not inside
-                    boundary_start = ""
-            elif inside:
-                #  print(x,y)
-                ninside += 1
-
-        pass
 
     #  print(l_loop)
     #  #  initialize outtermost boundary first
diff --git a/src/python/18_rk.py b/src/python/18_rk.py
new file mode 100644
index 0000000..cf219ca
--- /dev/null
+++ b/src/python/18_rk.py
@@ -0,0 +1,174 @@
+#!/usr/bin/env python3
+import sys
+import util
+import math
+
+def parse():
+    l = []
+    with open(sys.argv[1], 'r') as infile:
+        for line in infile:
+            line = line.strip()
+            di, step, color = line.split()
+            color = color[2:-1]
+            l.append((di, int(step), color))
+    return l
+
+def decode(color):
+    return int(color[:5], 16), util.diDecode[int(color[5])]
+
+
+def getSign(prev_di, di):
+    if prev_di == "R" and di == "D" or prev_di == "U" and di == "L":
+        return "7"
+    elif prev_di == "R" and di == "U" or prev_di == "D" and di == "L":
+        return "J"
+    elif prev_di == "L" and di == "D" or prev_di == "U" and di == "R":
+        return "F"
+    elif prev_di == "L" and di == "U" or prev_di == "D" and di == "R":
+        return "L"
+
+def sol(l, sol1 = True):
+    maxr, maxc = -math.inf, -math.inf
+    minr, minc = math.inf, math.inf
+    output = 0
+    pos = (0, 0)
+    for di, s, color in l:
+        if not sol1:
+            s, di = decode(color)
+        pos = util.tuple_add(pos, util.tuple_mul(util.direction_map[di], s)) 
+        output += s
+        maxr = max(maxr, pos[0])
+        maxc = max(maxc, pos[1])
+        minr = min(minr, pos[0])
+        minc = min(minc, pos[1])
+    assert pos == (0, 0)
+
+    nr = int(maxr-minr+1)
+    nc = int(maxc-minc+1)
+
+    #  a projection of (minr, minc) --> (0, 0)
+
+    pos = (-minr, -minc)
+
+    l_loop = util.matrix([[0 for j in range(nc)] for i in range(nr)])
+    m = util.matrix([["." for j in range(nc)] for i in range(nr)])
+    #  print(l_loop, m, sep="\n")
+
+
+    # sort out the starting point first
+    prev_di = ""
+    for di, s, color in l:
+        if not sol1:
+            s, di = decode(color)
+        if prev_di != "":
+            m[pos] = getSign(prev_di, di)
+        for i in range(s):
+            pos = util.tuple_add(pos, util.direction_map[di]) 
+            l_loop[pos] = 1
+
+            if di == "D" or di == "U":
+                m[pos] = "|"
+            elif di == "L" or di == "R":
+                m[pos] = "-"
+
+            pass
+        prev_di = di
+        pass
+    m[pos] = getSign(l[-1][0], l[0][0])
+    #  print(pos, m[pos])
+
+    #  print(l_loop, m, sep="\n")
+
+    output += util.calculate_inside(l_loop, m)
+    return output
+
+def sol2(l, sol2=True):
+    maxr, maxc = -math.inf, -math.inf
+    minr, minc = math.inf, math.inf
+    l_boundary = {0:{}}
+    output = 0
+    pos = (0, 0)
+    first_di = None
+    prev_di = None
+    for di, s, color in l:
+        if sol2:
+            s, di = decode(color)
+        if not first_di:
+            first_di = di
+
+        # correct the turning point
+        if prev_di != "":
+            l_boundary[pos[0]][pos[1]] = getSign(prev_di, di)
+
+        prev_di = di
+        if di == "U" or di == "D":
+            for i in range(s):
+                pos = util.tuple_add(pos, util.direction_map[di]) 
+                if pos[0] in l_boundary:
+                    l_boundary[pos[0]][pos[1]] = "|"
+                else:
+                    l_boundary[pos[0]] = {pos[1]:"|"}
+        else:
+            pos = util.tuple_add(pos, util.tuple_mul(util.direction_map[di], s)) 
+            pass
+
+        output += s
+        maxr = max(maxr, pos[0])
+        maxc = max(maxc, pos[1])
+        minr = min(minr, pos[0])
+        minc = min(minc, pos[1])
+        pass
+    assert pos == (0, 0)
+
+    l_boundary[0][0] = getSign(prev_di, first_di)
+    #  print(l_boundary)
+    #  print(l_boundary[0][0])
+
+    inside = False
+    s_prevline = 0
+    l_prevline = None
+    for r in range(minr, maxr+1):
+        lb = sorted([(i, j) for i, j in  l_boundary[r].items()], key = lambda x:x[0])
+        #  print(lb)
+        if l_prevline == lb:
+            output += s_prevline
+            continue
+        s_prevline = 0
+        l_prevline = lb
+
+        ib = 0
+        l_group = []
+        inside = False
+        true_next = False
+        prev_type_bound = None
+        prev_pos   = None
+        for ib in range(len(lb)-1):
+            p1, s1 = lb[ib]
+            p2, s2 = lb[ib+1]
+            dist = p2-p1-1
+
+            if s1+s2 in ["F7", "LJ"]:
+                true_next = False
+                continue
+            elif s1 == "|" or true_next:
+                true_next = False
+                inside = not inside
+            elif s1+s2 in ["FJ", "L7"]:
+                true_next = True
+                continue
+
+            if inside:
+                s_prevline += dist
+        output += s_prevline
+        #  print(output, s_prevline)
+    return output
+
+def main():
+    l = parse()
+    #  print(l)
+    #  print(sol(l))
+    print(sol2(l, False))
+    print(sol2(l))
+    pass
+
+main()
diff --git a/src/python/util.py b/src/python/util.py
new file mode 100644
index 0000000..6041deb
--- /dev/null
+++ b/src/python/util.py
@@ -0,0 +1,89 @@
+class matrix:
+    def __init__(self, l):
+        self._l = [[e for e in il] for il in l]
+
+    def dim(self):
+        return len(self._l), len(self._l[0])
+
+    def __iter__(self):
+        for x in self._l:
+            yield x
+
+
+    def __getitem__(self, tup):
+        if type(tup) == type((0,0)):
+            return self._l[tup[0]][tup[1]]
+        else:
+            return self._l[tup]
+
+    def __setitem__(self, tup, val):
+        self._l[tup[0]][tup[1]] = val
+
+    def __str__(self):
+        s = ""
+        for l in self:
+            for e in l:
+                s += str(e)
+            s += "\n"
+        return s
+
+def tuple_add(a, b):
+    return (a[0]+b[0], a[1]+b[1])
+
+def tuple_mul(a, b):
+    return (a[0]*b, a[1]*b)
+
+diDecode = [
+        "R", "D", "L", "U"
+        ]
+
+direction_map = {
+        "r":(0,  1),
+        "d":(1,  0),
+        "l":(0, -1),
+        "u":(-1, 0),
+
+        "R":(0,  1),
+        "D":(1,  0),
+        "L":(0, -1),
+        "U":(-1, 0),
+    }
+
+
+# day 10
+def calculate_inside(l_loop, m):
+    """
+    l_loop is the matrix where 1 is boundary, 0 is anything else
+    m is the whole matrix (list of list/str), but only boundary part will be accessed
+    """
+    ninside = 0
+    for x, line in enumerate(l_loop):
+        boundary_start = ""
+        inside = False
+        #  print(line)
+        for y, boundary in enumerate(line):
+            if boundary:
+                t = m[x][y]
+                #  print(t)
+                if t == "|":
+                    #  print("flip")
+                    inside = not inside
+                elif boundary_start == "":
+                    #  print("start with ", t)
+                    # this can't be '-'
+                    boundary_start = t
+                elif t != "-":
+                    # skip over -
+                    #  print("end in", t)
+                    #  print(f"{boundary_start}{t}")
+                    if f"{boundary_start}{t}" in ["FJ", "L7"]:
+                        #  print("flip")
+                        # flip only in those cases
+                        inside = not inside
+                    boundary_start = ""
+            elif inside:
+                #  print(x,y)
+                ninside += 1
+
+        pass
+    return ninside