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(jié)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(jié)點沒有右孩子，且當(dāng)前的結(jié)點有左或右孩子，直接返回false
        // 如果當(dāng)前結(jié)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(dāng)前結(jié)點沒有右孩子，那么之后層遍歷到的結(jié)點必須為葉子結(jié)點
      }
    }
    return true;
  }
}