For then-queens problem we observe that some solutions are simply reflections or rotations of others. For example when n = 4 the two solutions given below are equivalent under reflection.

1

2

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4

1

2

3

4

Observe that for finding inequivalent solutions the algorithm need only set X(l) = 2, 3, ... , [n/2] . Modify procedure NQUEENS so that only inequivalent solutions are computed.