Java | Leetcode Java题解之第52题N皇后II

题目：

题解：

class Solution {
    public int totalNQueens(int n) {
        Set columns = new HashSet();
        Set diagonals1 = new HashSet();
        Set diagonals2 = new HashSet();
        return backtrack(n, 0, columns, diagonals1, diagonals2);
    }

    public int backtrack(int n, int row, Set columns, Set diagonals1, Set diagonals2) {
        if (row == n) {
            return 1;
        } else {
            int count = 0;
            for (int i = 0; i < n; i++) {
                if (columns.contains(i)) {
                    continue;
                }
                int diagonal1 =