判断两个无向图是否同构的 graphHash 函数，横线处（把邻居编号拼入哈希串）应填入：
sort(neighbors.begin(), neighbors.end());
string hash;
for (int neighbor : neighbors) {
________ // 填入选项
}
nodeHashes[i] = hash;
- A. hash += to_string(neighbor);
- B. hash += to_string(neighbors);
- C. hash += to_string(neighbor) + ",";
- D. hash -= to_string(neighbors);
正确答案：C