二叉树 Z 字型遍历

Answer 1

考察点：遍历

public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
        List<List<Integer>> res =new ArrayList<List<Integer>>();
        LinkedList<TreeNode> l = new LinkedList<TreeNode>();
        boolean flag = true;
        if (root == null) {
            return res;
        }
        l.add(root);
        while (l.size() != 0) {
            flag = !flag;
            int size = l.size();
            List<Integer> list = new ArrayList<Integer>();
            for (int i = 0; i < size; i++) {
                TreeNode temp = l.remove();
                list.add(temp.val);
                if (temp.left != null)
					l.add(temp.left);
                if (temp.right != null)
					l.add(temp.right);
            }
            if (flag) {
                Collections.reverse(list);
            }
            res.add(list);
        }
        return res;
    }