102.binary-tree-level-order-traversal.cpp

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