I know AC solution that answers 4 for sequence starting from the following:

b2
h8
c3
a1

It is wrong. Neither black a1 can "jump over" white b2 (because c3 is not free) nor white b2 can "jump over" black a1 (because there is no cell behind a1).

I even know AC solution that answers 4 for input starting

a1
d4
b2
c3

It is wrong because b2 cannot jump over c3 (d4 is not empty) and c3 cannot jump over b2 (a1 is not empty).

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