diff --git a/d15/draw.py b/d15/draw.py
new file mode 100644
index 0000000..9b8eaf5
--- /dev/null
+++ b/d15/draw.py
@@ -0,0 +1,40 @@
+import sys
+from collections import defaultdict
+
+
+S = set()
+B = set()
+P = dict()
+Q = defaultdict(list)
+
+for l in sys.stdin.read().splitlines():
+    (_,_,X,Y,_,_,_,_,A,J) = l.split(" ")
+    x = int(X[2:-1])
+    y = int(Y[2:-1])
+    a = int(A[2:-1])
+    b = int(J[2:])
+    S.add((x,y))
+    B.add((a,b))
+    P[(x,y)] = (a,b)
+    Q[(a,b)].append((x,y))
+
+if False:
+    print("digraph G {")
+    print("overlap = false;")
+    def toid(x):
+        (x,y) = x
+        return str(x).replace("-","m")+"_"+str(y).replace("-","m")
+    for (k,v) in P.items():
+        print("S_"+toid(k), "->", "B_"+toid(v),";")
+    print('}')
+
+if True:
+    print("digraph G {")
+    print("overlap = false;")
+    def toid(x):
+        (x,y) = x
+        return str(x).replace("-","m")+"_"+str(y).replace("-","m")
+    for (k,V) in Q.items():
+        for v in V:
+            print("B_"+toid(k), "->", "C_"+toid(v),";")
+    print('}')
diff --git a/d15/part1.py b/d15/part1.py
new file mode 100644
index 0000000..90fb93e
--- /dev/null
+++ b/d15/part1.py
@@ -0,0 +1,52 @@
+import sys
+from collections import defaultdict
+
+BX = 1765036
+BY = 2000000
+
+def mtn(P,Q):
+    (x,y) = P
+    (u,v) = Q
+    return abs(u-x)+abs(v-y)
+
+S = set()
+B = set()
+P = dict()
+Q = defaultdict(list)
+
+for l in sys.stdin.read().splitlines():
+    (_,_,X,Y,_,_,_,_,A,J) = l.split(" ")
+    x = int(X[2:-1])
+    y = int(Y[2:-1])
+    a = int(A[2:-1])
+    b = int(J[2:])
+    S.add((x,y))
+    B.add((a,b))
+    P[(x,y)] = (a,b)
+    Q[(a,b)].append((x,y))
+
+if len(S) < 20:
+    BX = 2
+    BY = 10
+    
+
+Xs = set()
+for s in S:
+    (x,y) = s
+    sB = P[s] # nearest bc
+    dB = mtn(s,sB)  # max range before first bc
+    dy = abs(y-BY)  # to reach THE bc
+    r = dB - dy
+    if len(S) < 20:
+        print(s, sB, (BX,BY), dB, dy, r) 
+    if r > 0:
+        for d in range(-r,r+1):
+            nx = x+d
+            if abs(nx-BX)>=0:
+                Xs.add(nx)
+
+print(len(Xs)-1)
+
+if len(S) < 20:
+    print(Xs)
+
diff --git a/d15/part2a.py b/d15/part2a.py
new file mode 100644
index 0000000..1e8d1a6
--- /dev/null
+++ b/d15/part2a.py
@@ -0,0 +1,53 @@
+import sys
+from collections import defaultdict
+
+
+W = H = 4*1000*1000+1
+
+def mtn(P,Q):
+    (x,y) = P
+    (u,v) = Q
+    return abs(u-x)+abs(v-y)
+
+P = dict()
+
+for l in sys.stdin.read().splitlines():
+    (_,_,X,Y,_,_,_,_,A,J) = l.split(" ")
+    x = int(X[2:-1]) #+ 2
+    y = int(Y[2:-1])
+    a = int(A[2:-1]) #+ 2
+    b = int(J[2:])
+    P[(x,y)] = (a,b)
+
+if len(P) < 20:
+    print("S -> B", P)
+
+
+if len(P) < 20:
+    W = H = 30
+
+M = [ [1 for _ in range(W) ] for _ in range(H) ]
+    
+
+for s,sB in P.items():
+    (x,y) = s
+    dB = mtn(s,sB)  # max range before first bc
+    if len(P) < 20:
+        print(s, sB, dB)
+    for rx in range(dB+1):
+        for ry in range(dB-rx+1):
+            for (nx,ny) in [(x-rx,y-ry),(x-rx,y+ry),(x+rx,y-ry),(x+rx,y+ry)]:
+                if nx>=0 and nx<W and ny>=0 and ny<H:
+                    M[ny][nx] = 0
+
+for y,r in enumerate(M):
+    for x,c in enumerate(r):
+        if c == 0:
+            if len(P)>20:
+                print(x,y)
+            pass
+
+if len(P) < 20:
+    print("\n".join(" ".join(str(i) for i in l) for l in M))
+
+# take too much memory
diff --git a/d15/part2b.py b/d15/part2b.py
new file mode 100644
index 0000000..df75a0f
--- /dev/null
+++ b/d15/part2b.py
@@ -0,0 +1,37 @@
+import sys
+from collections import defaultdict
+
+def mtn(P,Q):
+    (x,y) = P
+    (u,v) = Q
+    return abs(u-x)+abs(v-y)
+
+S = list()
+for l in sys.stdin.read().splitlines():
+    (_,_,X,Y,_,_,_,_,A,J) = l.split(" ")
+    x = int(X[2:-1])
+    y = int(Y[2:-1])
+    a = int(A[2:-1])
+    b = int(J[2:])
+    S.append((x,y,abs(x-a)+abs(y-b)))
+
+print(S)
+
+W = H = 4*1000*1000 #+1
+if len(sys.argv)>1:
+    W = H = 20+1
+
+for i in range(W):
+    print(".", end ='')
+    for j in range(H):
+        # is this point reachable by any sensor
+        r = False
+        for (x,y,db) in S:
+            dp = abs(x-i)+abs(y-j)
+            if dp <= db:
+                r = True
+                break
+        if not r:
+            print(i,j)
+
+# taking too long
diff --git a/d15/part2c.py b/d15/part2c.py
new file mode 100644
index 0000000..a07ce2b
--- /dev/null
+++ b/d15/part2c.py
@@ -0,0 +1,39 @@
+import sys
+
+W = H = 4_000_000
+if len(sys.argv)>1: # sample
+    W = H = 20
+
+# store position that are not reachable, row by row
+L = [ [(0,0) for _ in range(32)] for _ in range(H+1) ]
+
+
+for i,l in enumerate(sys.stdin.read().splitlines()):
+    (_,_,X,Y,_,_,_,_,A,J) = l.split(" ")
+    x = int(X[2:-1])
+    y = int(Y[2:-1])
+    a = int(A[2:-1])
+    b = int(J[2:])
+    d = abs(x-a)+abs(y-b)
+    for ny in range(y-d, y+d+1):
+        if ny>=0 and ny<=H:
+            dy = abs(ny-y)
+            dx = d-dy
+            L[ny][i] = (x-dx,x+dx)
+            #L[ny] = intesec(L[ny], (x-dy,x+dy))
+
+
+if len(sys.argv)>1: # sample
+    for l in L:
+        print(l)
+
+d=0
+for (y,I) in enumerate(L):
+    SI = sorted(I)
+    maxx = 0
+    for (a,b) in SI:
+        if a>maxx+1:
+            d+=1
+            print(y, maxx+1, (maxx+1)*4_000_000+y)
+        maxx = max(maxx,b)
+print(d) # should be 1