leetcode 102. Binary Tree Level Order Traversal

class Solution {
public:
vector<vector<int>> levelOrder(TreeNode* root)
{
vector<vector<int>>res;
if (root == nullptr)
{
return res;
}
queue<TreeNode*> queue;
queue.push(root);
while (!queue.empty())
{
int size = queue.size();
vector<int> temp;
for (int i = 0; i < size; i++)
{
TreeNode *p = queue.front();
queue.pop();
temp.push_back(p->val);
if (p->left)
{
queue.push(p->left);
}
if (p->right)
{
queue.push(p->right);
}
}
res.push_back(temp);
}
return res;
}
};