import java.util.*;class TreeNode {  int val = 0;  TreeNode left = null;  TreeNode right = null;  public TreeNode(int val) {    this.val = val;  }}public class CheckCompletion {  public boolean checking(TreeNode root) {    Queue<TreeNode> queue = new LinkedList<TreeNode>();    boolean leaf = false; // 葉子結點    TreeNode left;    TreeNode right;    queue.add(root);    while (!queue.isEmpty()) {      root = queue.poll();      left = root.left;      right = root.right;      if ((leaf&&(left!=null||right!=null)) || (left==null&&right!=null)) {        // 如果之前層遍歷的結點沒有右孩子，且當前的結點有左或右孩子，直接返回false        // 如果當前結點有右孩子卻沒有左孩子，直接返回false        return false;      }      if (left != null) {        queue.offer(root.left);      }      if (right != null) {        queue.offer(root.right);      }else {        leaf = false; // 如果當前結點沒有右孩子，那么之后層遍歷到的結點必須為葉子結點      }    }    return true;  }}