Check If Binary Tree Is Completed

/**
 * public class TreeNode {
 *   public int key;
 *   public TreeNode left;
 *   public TreeNode right;
 *   public TreeNode(int key) {
 *     this.key = key;
 *   }
 * }
 */
public class Solution {
  public boolean isCompleted(TreeNode root) {
    // Write your solution here
    if (root==null){
      return true;
    }
    Queue<TreeNode> q = new LinkedList<TreeNode>();
    q.offer(root);
    
    int isLeaf = 0;
    while(!q.isEmpty()){
      Queue<TreeNode> nextQ = new LinkedList<TreeNode>();
      int size = q.size();
      for(int i=0; i<size; i++){
        TreeNode curNode = q.poll();
        if(curNode.left==null && curNode.right!=null){
          return false;
        }
        if(curNode.left!=null){
          if(isLeaf==1){
            return false;
          }
          nextQ.offer(curNode.left);
        }
        if(curNode.right!=null){
          if(isLeaf==1){
            return false;
          }
          nextQ.offer(curNode.right);
        }
        if(curNode.left==null || curNode.right==null){
          isLeaf=1;
        }
      }
      q = nextQ;
    }
    return true;

  }
}