Ken's Puzzle of the Week

More Knight Swapping

A

B

 

 

 

 

 

C

D

E

F

G

 

 

 

 

H

I

J

 

 

 

 

K

L

M

N

O

 

 

 

 

 

P

Q

Put four white chess knights (a,b,c,d) onto squares (A,B,C,D).  Put four black chess knights (1,2,3,4) onto squares (N,O,P,Q).  Swap the positions of the knights using only knight moves.  Moves do not need to alternate in color and you may continue moving a single knight for many moves in succession.  At no time may a white and black knight attack one another.

Source: Original.

Solutions were received from Bernie R. Erickson.  He pointed out the puzzle is more easily solved by remapping the grid above into the map below. 
                   K
                /  |  \
      O ---- J     D     F
           /   \   |   /   \
   A ---- E     P  I  B     M ---- Q 
           \   /   |   \   /
             L     N     H ---- C
                \  |  /
                   G
My (Ken's) solution. Each move starts with the occupied square for reference.  There are probably shorter solutions.  This one uses 40 moves:
1:NGL d:DIN b:BFKDI c:CHBFK 4:QMHC c:KFMQ 3:PJKFB 1:LPJK a:AELG 2:OJEA a:GLP d:NGL b:IN 1:KD a:PJO d:LP
Update 2Sept2008, Nyles Heise sent this 36 move solution (some moves could be combined for a single piece to keep moving.)
  0           
a b           
c d . . .     
    . . .     
    . . . 1 2 
          3 4 
              
 1 b:BF       
a ,           
c d . b .     
    . . .     
    . . . 1 2 
          3 4 
              
 2 c:CH       
a .           
, d . b .     
    c . .     
    . . . 1 2 
          3 4 
              
 3 b:FK       
a .           
. d . , .     
    c . .     
    b . . 1 2 
          3 4 
              
 4 c:HB       
a c           
. d . . .     
    , . .     
    b . . 1 2 
          3 4 
              
 5 c:BF       
a ,           
. d . c .     
    . . .     
    b . . 1 2 
          3 4 
              
 6 1:NG       
a .           
. d . c 1     
    . . .     
    b . . , 2 
          3 4 
              
 7 d:DI       
a .           
. , . c 1     
    . d .     
    b . . . 2 
          3 4 
              
 8 b:KD       
a .           
. b . c 1     
    . d .     
    , . . . 2 
          3 4 
              
 9 c:FK       
a .           
. b . , 1     
    . d .     
    c . . . 2 
          3 4 
              
10 4:QM       
a .           
. b . . 1     
    . d .     
    c . 4 . 2 
          3 , 
              
11 4:MH       
a .           
. b . . 1     
    4 d .     
    c . , . 2 
          3 . 
              
12 c:KF       
a .           
. b . c 1     
    4 d .     
    , . . . 2 
          3 . 
              
13 4:HC       
a .           
4 b . c 1     
    , d .     
    . . . . 2 
          3 . 
              
14 c:FM       
a .           
4 b . , 1     
    . d .     
    . . c . 2 
          3 . 
              
15 c:MQ       
a .           
4 b . . 1     
    . d .     
    . . , . 2 
          3 c 
              
16 1:GH       
a .           
4 b . . ,     
    1 d .     
    . . . . 2 
          3 c 
              
17 d:IN       
a .           
4 b . . .     
    1 , .     
    . . . d 2 
          3 c 
              
18 b:DI       
a .           
4 , . . .     
    1 b .     
    . . . d 2 
          3 c 
              
19 1:HB       
a 1           
4 . . . .     
    , b .     
    . . . d 2 
          3 c 
              
20 3:PJ       
a 1           
4 . . . .     
    . b 3     
    . . . d 2 
          , c 
              
21 3:JK       
a 1           
4 . . . .     
    . b ,     
    3 . . d 2 
          . c 
              
22 a:AE       
, 1           
4 . a . .     
    . b .     
    3 . . d 2 
          . c 
              
23 a:EL       
. 1           
4 . , . .     
    . b .     
    3 a . d 2 
          . c 
              
24 a:LG       
. 1           
4 . . . a     
    . b .     
    3 , . d 2 
          . c 
              
25 2:OJ       
. 1           
4 . . . a     
    . b 2     
    3 . . d , 
          . c 
              
26 2:JE       
. 1           
4 . 2 . a     
    . b ,     
    3 . . d . 
          . c 
              
27 2:EA       
2 1           
4 . , . a     
    . b .     
    3 . . d . 
          . c 
              
28 a:GL       
2 1           
4 . . . ,     
    . b .     
    3 a . d . 
          . c 
              
29 a:LP       
2 1           
4 . . . .     
    . b .     
    3 , . d . 
          a c 
              
30 d:NG       
2 1           
4 . . . d     
    . b .     
    3 . . , . 
          a c 
              
31 d:GL       
2 1           
4 . . . ,     
    . b .     
    3 d . . . 
          a c 
              
32 b:IN       
2 1           
4 . . . .     
    . , .     
    3 d . b . 
          a c 
              
33 3:KD       
2 1           
4 3 . . .     
    . . .     
    , d . b . 
          a c 
              
34 a:PJ       
2 1           
4 3 . . .     
    . . a     
    . d . b . 
          , c 
              
35 a:JO       
2 1           
4 3 . . .     
    . . ,     
    . d . b a 
          . c 
              
36 d:LP       
2 1           
4 3 . . .     
    . . .     
    . , . b a 
          d c
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