给定一个二叉树，返回每一层中最大的节点值，结果以数组形式返回，横线处应填入（）。
#include <vector>
#include <queue>
#include <algorithm>
struct TreeNode {
int val;
TreeNode* left;
TreeNode* right;
TreeNode(int x): val(x), left(nullptr), right(nullptr) {}
};
vector<int> largestValues(TreeNode* root) {
vector<int> result;
if (!root) return result;
queue<TreeNode*> q;
q.push(root);
while (!q.empty()) {
int sz = q.size();
int maxVal = INT_MIN;
for (int i = 0; i < sz; ++i) {
TreeNode* node;
____________
maxVal = max(maxVal, node->val);
if (node->left) q.push(node->left);
if (node->right) q.push(node->right);
}
result.push_back(maxVal);
}
return result;
}
- A. ```cpp
node = q.end();
- **B.** ```cpp
node = q.front();
- C. ```cpp
q.pop();
node = q.front();
- **D.** ```cpp
node = q.front();
q.pop();