Design hashset

Design a HashSet without using any built-in hash table libraries.

To be specific, your design should include these functions:

add(value): Insert a value into the HashSet. 
contains(value) : Return whether the value exists in the HashSet or not.
remove(value): Remove a value in the HashSet. If the value does not exist in the HashSet, do nothing.

Example:

MyHashSet hashSet = new MyHashSet();
hashSet.add(1);         
hashSet.add(2);         
hashSet.contains(1);    // returns true
hashSet.contains(3);    // returns false (not found)
hashSet.add(2);          
hashSet.contains(2);    // returns true
hashSet.remove(2);          
hashSet.contains(2);    // returns false (already removed)

Note:

All values will be in the range of [0, 1000000].
The number of operations will be in the range of [1, 10000].
Please do not use the built-in HashSet library.

这题让设计一个hashset，并且不能用现成的数据结构。这里直接用位操作来模拟，位操作占用的内存应当是比较小的。

class MyHashSet {
public:
  /** Initialize your data structure here. */
  MyHashSet() { memset(vals_, 0, sizeof(vals_)); }

  void add(int key) {
      int index = key / 64;
      int offset = key % 64;

      vals_[index] |= ((uint64_t)1 << offset);
  }

  void remove(int key) {
      int index = key / 64;
      int offset = key % 64;

      vals_[index] &= (~((uint64_t)1 << offset));
  }

  /** Returns true if this set contains the specified element */
  bool contains(int key) {
      int index = key / 64;
      int offset = key % 64;

      return (vals_[index] & ((uint64_t)1 << offset)) != 0;
  }

private:
  uint64_t vals_[15625];
};