public int totalNQueens(int n) {
StringBuilder[] board = new StringBuilder[n];
for (int i = 0; i < n; i++) {
board[i] = new StringBuilder();
for (int j = 0; j < n; j++) {
board[i].append('.');
}
}
for (int i = 0; i < n / 2; i++) {
board[0].setCharAt(i, 'Q');
dfs(n, 1, board);
board[0].setCharAt(i, '.');
}
ArrayList<String[]> aux = new ArrayList<String[]>();
for (String[] k : res) {
String[] tmp = new String[n];
for (int i = 0; i < n; i++) {
StringBuilder sb = new StringBuilder(k[i]).reverse();
tmp[i] = sb.toString();
}
aux.add(tmp);
}
res.addAll(aux);
if (n % 2 != 0) {
board[0].setCharAt(n / 2, 'Q');
dfs(n, 1, board);
board[0].setCharAt(n / 2, '.');
}
return res.size();
}
public static ArrayList<String> serializeTree(TreeNode tree) {
ArrayList<String> res = new ArrayList<>();
LinkedList<TreeNode> queue = new LinkedList<>();
queue.addLast(tree);
while (!queue.isEmpty()) {
TreeNode node = queue.removeFirst();
if (node == null) {
res.add(NULL);
} else {
res.add(String.valueOf(node.val));
queue.add(node.left);
queue.add(node.right);
}
}
while (res.size() > 1 && res.get(res.size() - 1).equals(NULL)) {
res.remove(res.size() - 1);
}
return res;
}