queue<TreeNode*> find_level(queue<TreeNode*>q){
queue<TreeNode*>res;
while(!q.empty()) {
TreeNode* top = q.front();
q.pop();
if(top==NULL) continue;
res.push(top->left);
res.push(top->right);
}
return res;
}
這是將NULL結點也放進去的版本(上面)