How to identify whether or not std::unordered_map has experienced hash collisions?

问题

How to identify whether or not the keys in a std::unordered_map have experienced hash collisions?

That is, how to identify if any collision chaining is present?

回答1:

You can use the bucket interface and its bucket_size method.

std::unordered_map<int, int> map;
bool has_collision = false;

for(size_t bucket = 0; bucket < map.bucket_count(); bucket++) {
    if(map.bucket_size(bucket) > 1) {
        has_collision = true;
        break;
    }
}

来源：https://stackoverflow.com/questions/46137811/how-to-identify-whether-or-not-stdunordered-map-has-experienced-hash-collision