【剑指offer】-从上往下打印二叉树-22/67

public static ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
    ArrayList<Integer> arrayList = new ArrayList<Integer>(); // 存储遍历的数组
    Queue<TreeNode> queue = new LinkedList<TreeNode>();
    if (root == null) {
      return arrayList;
    }
    queue.add(root);
    while (queue.size() != 0) {
      TreeNode temp = queue.poll();
      if(temp.left != null) {
        queue.add(temp.left);
      }
      if(temp.right != null) {
        queue.add(temp.right);
      }
      arrayList.add(temp.val);
    }
    return arrayList;
  }