求解n皇后问题。给定一个N×N的棋盘，在棋盘上放置N个皇后，使得N个皇后两两之间互不攻击。任何两个处于同一列，同一行，同一对角线上的皇后都会互相攻击。

-Solve the n queens problem. To set a NN board, place N queens on a chessboard, making the N-queens do not attack each other between every two. Any two in the same column, same row, the Queen will attack each other on the same diagonal.