c++ - 使用键值对为零的 k 个桶初始化 c++14 unordered_map

Question

我正在尝试创建一个具有最小初始桶数 (k) 的 unordered_map，所有键值对都初始化为零。稍后，它应该进入 for 循环并打印值。

int someFunction(int k){
  unordered_map<int, int> majority(k, {0,0});
}

for(auto m : majority){
  cout << m.first << " " <<  m.second << " \n";
}

我得到以下编译(c++ 14)错误:

no matching function for call to ‘std::unordered_map<int, int>::unordered_map(int&, <brace-enclosed initializer list>)

有什么办法可以实现吗？

Answer 1

unordered_map 表示哈希数据结构。根据散列定义，每个键都必须是唯一的。所以你不能用几个零 int 键来初始化 majority。相反，您可以使用保留功能:

void reserve ( size_type n );

Request a capacity change

Sets the number of buckets in the container (bucket_count) to the most appropriate to contain at least n elements.

If n is greater than the current bucket_count multiplied by the max_load_factor, the container's bucket_count is increased and a rehash is forced.

If n is lower than that, the function may have no effect.