146.Design HashSet

题目：

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

在不使用任何内置哈希表库的情况下设计HashSet。

To be specific, your design should include these functions:

具体而言，您的设计应包括以下功能：

• add(value): Insert a value into the HashSet. 将值插入HashSet。
• contains(value) : Return whether the value exists in the HashSet or not.返回值是否存在于HashSet中。
• remove(value): Remove a value in the HashSet. If the value does not exist in the HashSet, do nothing.删除HashSet中的值。 如果HashSet中不存在该值，则不执行任何操作。

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].所有值都在[0,1000000]范围内。
• The number of operations will be in the range of [1, 10000].操作次数将在[1,10000]范围内。
• Please do not use the built-in HashSet library.请不要使用内置的HashSet库。

解答：

class MyHashSet {
    private int buckets=1000;
    private int itemsPerBucket=1001;
    private boolean[][] table;

    /** Initialize your data structure here. */
    public MyHashSet() {
        table=new boolean[buckets][];
    }
    
    public int hash(int key){
        return key%buckets;
    }
    
    public int pos(int key){
        return key/buckets;
    }
    
    public void add(int key) {
        int hashkey=hash(key);
        if(table[hashkey]==null)
            table[hashkey]=new boolean[itemsPerBucket];
        table[hashkey][pos(key)]=true;
    }
    
    public void remove(int key) {
        int hashkey=hash(key);
        if(table[hashkey]!=null)
            table[hashkey][pos(key)]=false;
    }
    
    /** Returns true if this set contains the specified element */
    public boolean contains(int key) {
        int hashkey=hash(key);
        if(table[hashkey]!=null&&table[hashkey][pos(key)])
            return true;
        return false;
    }
}

/**
 * Your MyHashSet object will be instantiated and called as such:
 * MyHashSet obj = new MyHashSet();
 * obj.add(key);
 * obj.remove(key);
 * boolean param_3 = obj.contains(key);
 */

详解：