Find the rightmost node value at each level of a binary tree. Serialize each level and output the last node of each level.

class Solution {
public:
    vector<int> rightSideView(TreeNode* root) {
        vector<int> ans(0);
        if (NULL == root)
        {
            return ans;
        }
        queue<TreeNode *> qList;
        qList.push(root);
        while (qList.size() > 0)
        {
            int size = qList.size();
            for (int i = 0;i < size;i++)
            {
                TreeNode * head = qList.front();
                if (NULL != head->left)
                {
                    qList.push(head->left);
                }
                if (NULL != head->right)
                {
                    qList.push(head->right);
                }
                qList.pop();
                if (i == size-1)
                {
                    ans.push_back(head->val);
                }
            }
        }
        return ans;
    }
};