diff --git a/AoC2021/code/AoC23.py b/AoC2021/code/AoC23.py
new file mode 100755
index 0000000..c0ea67a
--- /dev/null
+++ b/AoC2021/code/AoC23.py
@@ -0,0 +1,109 @@
+#!/usr/bin/env python3
+
+import sys
+from functools import cache
+
+@cache
+def path(f1,f2):
+    path = []
+    y, x = f1
+    while y != 0:
+        y -= 1
+        path.append((y,x))
+    while x != f2[1]:
+        x += 1 if f2[1] > x else -1
+        path.append((y,x))
+    while y != f2[0]:
+        y += 1
+        path.append((y,x))
+    assert path[-1] == f2
+    return path
+
+def pathvalid(path,board):
+    for p in path:
+        if p in board: return False
+    return True
+
+def cost(a,w):
+    if a == 'A': return len(w) * 1
+    if a == 'B': return len(w) * 10
+    if a == 'C': return len(w) * 100
+    if a == 'D': return len(w) * 1000
+
+def endstate(board):
+    for f,a in board.items():
+        if f[1] != target[a]: return False
+    return True
+
+def target_position(f,b,lowest):
+    a = b[f]
+    if f[1] != target[a]: return False
+    for y in range(f[0],lowest+1):
+        if (y,target[a]) not in b: return False
+        if b[(y,target[a])] != a: return False
+    return True
+
+def totarget(board,lowest):
+    change = False
+    costs = 0
+    nb = {k: v for k,v in board.items()}
+    for f,a in board.items():
+        if target_position(f,nb,lowest): continue
+        t = (lowest,target[a])
+        while t in nb and nb[t] == a:
+            t = (t[0]-1,target[a])
+        if t == (0,target[a]): continue
+        p = path(f,t)
+        if pathvalid(p,nb):
+            change = True
+            nb.pop(f)
+            nb[t] = a
+            costs += cost(a,p)
+    return nb,costs,change
+
+def dfs(board,lowest,costs=0,curmin=sys.maxsize):
+    ch = True
+    nb = {k: v for k,v in board.items()}
+    while ch:
+        nb,co,ch = totarget(nb,lowest)
+        costs += co
+    if endstate(nb): 
+        return costs
+    if costs > curmin: return None
+    board = {k: v for k,v in nb.items()}
+    for f,a in board.items():
+        if f[0] != 0 and not(target_position(f,board,lowest)):
+            for f2 in hallway:
+                p = path(f,f2)
+                if pathvalid(p, board):
+                    cb = {k: v for k,v in board.items()}
+                    cb.pop(f)
+                    cb[f2] = a
+                    nc = dfs(cb,lowest,costs+cost(a,p),curmin)
+                    if nc is not None and nc < curmin: curmin = nc
+    if curmin < sys.maxsize: return curmin
+
+if __name__ == '__main__':
+    # challenge 1
+    lines = open(sys.argv[1]).readlines()
+    start = {}
+    for y,l in enumerate(lines[1:]):
+        for x,f in enumerate(l[1:]):
+            if f in 'ABCD': start[(y,x)] = f 
+
+    hallway = [(0,0), (0,1), (0,3), (0,5), (0,7), (0,9), (0,10)]
+    target = {'A': 2, 'B': 4, 'C': 6, 'D': 8}
+
+    res1 = str(dfs(start,2))
+    print("challenge 1:" + "\n" +  res1 + "\n")
+
+    # challenge 2
+    lines = open(sys.argv[2]).readlines()
+    start = {}
+    for y,l in enumerate(lines[1:]):
+        for x,f in enumerate(l[1:]):
+            if f in 'ABCD': start[(y,x)] = f 
+
+    res2 = str(dfs(start,4))
+    print("challenge 2:" + "\n" +  res2 + "\n")
+
diff --git a/AoC2021/inputs/input23 b/AoC2021/inputs/input23
new file mode 100644
index 0000000..6cda201
--- /dev/null
+++ b/AoC2021/inputs/input23
@@ -0,0 +1,5 @@
+#############
+#...........#
+###A#C#B#A###
+  #D#D#B#C#
+  #########
diff --git a/AoC2021/inputs/input23-2 b/AoC2021/inputs/input23-2
new file mode 100644
index 0000000..534f76f
--- /dev/null
+++ b/AoC2021/inputs/input23-2
@@ -0,0 +1,7 @@
+#############
+#...........#
+###A#C#B#A###
+  #D#C#B#A#
+  #D#B#A#C#
+  #D#D#B#C#
+  #########
diff --git a/AoC2021/inputs/test23 b/AoC2021/inputs/test23
new file mode 100644
index 0000000..6a7120d
--- /dev/null
+++ b/AoC2021/inputs/test23
@@ -0,0 +1,5 @@
+#############
+#...........#
+###B#C#B#D###
+  #A#D#C#A#
+  #########
diff --git a/AoC2021/inputs/test23-2 b/AoC2021/inputs/test23-2
new file mode 100644
index 0000000..1e769e1
--- /dev/null
+++ b/AoC2021/inputs/test23-2
@@ -0,0 +1,7 @@
+#############
+#...........#
+###B#C#B#D###
+  #D#C#B#A#
+  #D#B#A#C#
+  #A#D#C#A#
+  #########
diff --git a/AoC2021/inputs/test23-3 b/AoC2021/inputs/test23-3
new file mode 100644
index 0000000..647c803
--- /dev/null
+++ b/AoC2021/inputs/test23-3
@@ -0,0 +1,5 @@
+#############
+#.....D.D.A.#
+###.#B#C#.###
+  #A#B#C#.#
+  #########
diff --git a/AoC2021/inputs/test23-4 b/AoC2021/inputs/test23-4
new file mode 100644
index 0000000..d8dc3c9
--- /dev/null
+++ b/AoC2021/inputs/test23-4
@@ -0,0 +1,7 @@
+#############
+#AA.D......D#
+###B#.#C#.###
+  #D#B#C#.#
+  #D#B#C#.#
+  #A#B#C#A#
+  #########