n皇后问题的BFS算法，算法简洁，作为初学者一看就懂，不过先看会BFS算法很重要，这比普通的动态规划速度要快很多-N queens problem BFS algorithm, the algorithm is simple, as a beginner to understand, but first look at the BFS algorithm is very important, which is much faster than the general dynamic planni