Copyright (c) James A. Storer

Puzzle Contrast, Problem 4
(Go between the solutions for problems 1 and 2,
and exchange pieces X and Y.)

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Rectilinear Solution
      Rectilinear steps: 24
      Straight-Line steps: 26
      Unit steps: 38
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#0:
B B A A
Y     X
D D C C

#1. Move X west 2 units:
B B A A
Y X    
D D C C

#2. Move A south:
B B    
Y X A A
D D C C

#3. Move B east 2 units:
    B B
Y X A A
D D C C

#4. Move X on a path of 2 segments ending west:
X   B B
Y   A A
D D C C

#5. Move Y on a path of 2 segments ending north:
X Y B B
    A A
D D C C

#6. Move A west 2 units:
X Y B B
A A    
D D C C

#7. Move C north:
X Y B B
A A C C
D D    

#8. Move D east 2 units:
X Y B B
A A C C
    D D

#9. Move A south:
X Y B B
    C C
A A D D

#10. Move C west 2 units:
X Y B B
C C    
A A D D

#11. Move B south:
X Y    
C C B B
A A D D

#12. Move Y east 2 units:
X     Y
C C B B
A A D D

#13. Move X east 2 units:
    X Y
C C B B
A A D D

#14. Move C north:
C C X Y
    B B
A A D D

#15. Move B west 2 units:
C C X Y
B B    
A A D D

#16. Move D north:
C C X Y
B B D D
A A    

#17. Move A east 2 units:
C C X Y
B B D D
    A A

#18. Move B south:
C C X Y
    D D
B B A A

#19. Move D west 2 units:
C C X Y
D D    
B B A A

#20. Move X south:
C C   Y
D D X  
B B A A

#21. Move Y south:
C C    
D D X Y
B B A A

#22. Move C east 2 units:
    C C
D D X Y
B B A A

#23. Move D north:
D D C C
    X Y
B B A A

#24. Move X west 2 units:
D D C C
X     Y
B B A A