public class EightQueens {
    private static int N = 10;    //8皇后
    private static int[] X = new int[N + 1];    //每个皇后的位置
    private static int sum = 0;    //解法个数
    
    /*检查当前位置是否冲突*/
    public static boolean check(int n){
        for(int i = 1; i < n; i++)
            if(Math.abs(n - i) == Math.abs(X[n] - X[i]) || X[n] == X[i]) return false;
        return true;
    }
    
    /*t表示当前行数*/
    public static void backtrak(int t){
        if(t > N) sum++;
        else{
            for(int i = 1; i <= N; i++){
                X[t] = i;
                if(check(t)) backtrak(t+1);
            }
        }
    }
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        for(int i = 0; i <= N; i++){
            X[i] = 0;
        }
        backtrak(1);
        System.out.println(sum);
    }

}