N-Queens II leetcode

Follow up for N-Queens problem.

Now, instead outputting board configurations, return the total number of distinct solutions.

与N-Queens I 完全相同， 只是返回的是个数

ublic class Solution {
    public int totalNQueens(int n) {
        int[] res = new int[1];
        if (n <= 0) {
            return res[0];
        }
        int[] column = new int[n];
        helper(res, column, n, 0);
        return res[0];
    }
    public void helper(int[] res, int[] column, int n, int pos) {
        if (pos == n) {
            res[0]++;
        } else {
            for (int i = 0; i < n; i++) {
                column[pos] = i;
                if (isValid(column, pos)) {
                    helper(res,column, n, pos + 1);
                }
            }
        }
    }
    public boolean isValid(int[] column, int pos) {
        for (int i = 0; i < pos; i++) {
            if (column[i] == column[pos] || Math.abs(column[i] - column[pos]) == pos - i) {
                return false;
            }
        }
        return true;
    } 
}