# 705. Design HashSet 设计哈希集合

@TOC

## # 题目描述

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

To be specific, your design should include these two 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.contains(1);    // returns true
hashSet.contains(2);    // returns true
hashSet.remove(2);
hashSet.contains(2);    // returns false (already removed)
``````

Note:

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

## # 解题方法

### # 位图法

``````class MyHashSet:

def __init__(self):
"""
"""
self.buckets = 1000
self.itemsPerBucket = 1001
self.table = [[] for _ in range(self.buckets)]

def hash(self, key):
return key % self.buckets

def pos(self, key):
return key // self.buckets

"""
:type key: int
:rtype: void
"""
hashkey = self.hash(key)
if not self.table[hashkey]:
self.table[hashkey] = [0] * self.itemsPerBucket
self.table[hashkey][self.pos(key)] = 1

def remove(self, key):
"""
:type key: int
:rtype: void
"""
hashkey = self.hash(key)
if self.table[hashkey]:
self.table[hashkey][self.pos(key)] = 0

def contains(self, key):
"""
Returns true if this set did not already contain the specified element
:type key: int
:rtype: bool
"""
hashkey = self.hash(key)
return (self.table[hashkey] != []) and (self.table[hashkey][self.pos(key)] == 1)

# Your MyHashSet object will be instantiated and called as such:
# obj = MyHashSet()
# obj.remove(key)
# param_3 = obj.contains(key)
``````

### # 数组法

``````class MyHashSet:

def __init__(self):
"""
"""
self.set = [False] * 1000001

"""
:type key: int
:rtype: void
"""
self.set[key] = True

def remove(self, key):
"""
:type key: int
:rtype: void
"""
self.set[key] = False

def contains(self, key):
"""
Returns true if this set contains the specified element
:type key: int
:rtype: bool
"""
return self.set[key]

# Your MyHashSet object will be instantiated and called as such:
# obj = MyHashSet()