diff --git a/day23/input b/day23/input
new file mode 100644
index 0000000..b5abd49
--- /dev/null
+++ b/day23/input
@@ -0,0 +1,141 @@
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+#.#######.#.#.#.###.#.#.#.#.###.#.#.#.#.#####.#.#.#.#.#.###.#.#.###.#.###.#.#######.#.#.###.#.#####.#.#.#.###.#.#.#.#.###.#######.#.#.#.#.#.#
+#.........#...#.....#...#...###...#...#.......#...#...#.....#...###...###...#######...#.....#.......#...#.....#...#...###.........#...#...#.#
+###########################################################################################################################################.#
diff --git a/day23/sample1.in b/day23/sample1.in
new file mode 100644
index 0000000..ea945a4
--- /dev/null
+++ b/day23/sample1.in
@@ -0,0 +1,23 @@
+#.#####################
+#.......#########...###
+#######.#########.#.###
+###.....#.>.>.###.#.###
+###v#####.#v#.###.#.###
+###.>...#.#.#.....#...#
+###v###.#.#.#########.#
+###...#.#.#.......#...#
+#####.#.#.#######.#.###
+#.....#.#.#.......#...#
+#.#####.#.#.#########v#
+#.#...#...#...###...>.#
+#.#.#v#######v###.###v#
+#...#.>.#...>.>.#.###.#
+#####v#.#.###v#.#.###.#
+#.....#...#...#.#.#...#
+#.#########.###.#.#.###
+#...###...#...#...#.###
+###.###.#.###v#####v###
+#...#...#.#.>.>.#.>.###
+#.###.###.#.###.#.#v###
+#.....###...###...#...#
+#####################.#
diff --git a/day23/sol.py b/day23/sol.py
new file mode 100644
index 0000000..d830d2d
--- /dev/null
+++ b/day23/sol.py
@@ -0,0 +1,115 @@
+import sys
+input = sys.stdin
+map = []
+for line in input:
+    map.append(list(line.strip()))
+
+# construct a graph
+for i,c in enumerate(map[0]):
+    if c == '.':
+        start = (i,0)
+        break
+
+def neighbors(x,y):
+    n = []
+    c = map[y][x]
+    for i,j in [(y-1,x),(y+1,x),(y,x-1),(y,x+1)]:
+        if c == '<' and not j < x: continue
+        if c == '>' and not j > x: continue
+        if c == '^' and not i < y: continue
+        if c == 'v' and not i > y: continue
+        if 0 <= i < len(map) and 0 <= j < len(map[i]):
+            if map[i][j] != '#':
+                n.append((j,i))
+    return n
+
+spots = []
+for i in range(len(map)):
+    for j in range(len(map[i])):
+        if map[i][j] == '.':
+            n = neighbors(j,i)
+            if len(n) not in (0,2):
+                spots.append((j,i))
+
+def reachable(start,spots):
+    q = [(0,start)]
+    dist = {}
+    r = []
+    while q:
+        q.sort()
+        n,(x,y) = q.pop(0)
+        if (x,y) in dist:
+            continue
+        dist[x,y] = n
+        #print(x,y,neighbors(x,y))
+        if (x,y) in spots and (x,y) != start:
+                r.append((n,(x,y)))
+        else:
+            for j,i in neighbors(x,y):
+                if (j,i) not in dist:
+                    q.append((n+1,(j,i)))
+
+    return r
+
+G = {}
+for p in spots:
+    G[p] = reachable(p,spots)
+    
+print(G)
+
+
+def topo(G, start):
+    t = []
+    seen = set()
+    tmp = set()
+    def visit(n):
+        if n in seen:
+            return
+        if n in tmp:
+            raise Exception("cycle with %s %s"  % (repr(n),tmp))
+        tmp.add(n)
+        for _, p in G[n]:
+            visit(p)
+        tmp.remove(n)
+        seen.add(n)
+        t.append(n)
+    visit(start)
+    t.reverse()
+    return t
+
+print("topo=",topo(G,start))
+
+
+dist = {n:float('inf') for n in G}
+pred = {}
+dist[start] = 0
+T = topo(G, start)
+for u in T:
+    for n,v in G[u]:
+        w = -n
+        if dist[v] > dist[u] + w:
+            dist[v] = dist[u] + w
+        pred[v] = u
+    
+print(dist)
+print(-min(dist.values()))
+
+#import astar
+#def goal(state):
+#    x,y = state
+#    return y == len(map)-1
+#
+#M = max(n for p in G for n,_ in G[p])
+#
+#def nb(state):
+#    p = state
+#    for n,q in G[p]:
+#        yield 1+M-n, q
+#
+#n, g, path = astar.search(start, goal, nb)
+#print(g,path)
+#t = 0
+#for p, q in zip(path, path[1:]):
+#    t += sum(n for n,r in G[p] if r == q)
+#
+#print(t)