A puzzler for chess buffs is the Eight Queens problem, which asks: Is it possible to place eight queens on an empty chessboard so that no queen is “attacking” any other (i.e., no two queens are in the same row, in the same column or along the same diagonal)? For example, if a queen is placed in the upper-left corner of the board, no other queens could be placed in any of the marked squares shown in Fig. 18.21 . Solve the problem recursively.

Fig. 18.21

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