leetcode:705. 设计哈希集合(Java)

705.设计哈希集合
不使用任何内建的哈希表库设计一个哈希集合

具体地说，你的设计应该包含以下的功能

• add(value)：向哈希集合中插入一个值。
• contains(value) ：返回哈希集合中是否存在这个值
• remove(value)：将给定值从哈希集合中删除。如果哈希集合中没有这个值，什么也不做。

示例:

MyHashSet hashSet = new MyHashSet();
hashSet.add(1);         
hashSet.add(2);         
hashSet.contains(1);    // 返回 true
hashSet.contains(3);    // 返回 false (未找到)
hashSet.add(2);          
hashSet.contains(2);    // 返回 true
hashSet.remove(2);          
hashSet.contains(2);    // 返回  false (已经被删除)

方法1：用时比较慢，但代码是基础

class MyHashSet {
    class Node {
        public int key;
        public Node next;

        public Node(int key) {
            this.key = key;
        }
    }
    private Node[] array;
    private int usedSize;
    /** Initialize your data structure here. */
    public MyHashSet() {
        this.array = new Node[10];
        this.usedSize = 0;
    }
    
    public void add(int key) {
        // 1. 得到key对应的唯一的hashCode()所得到的下标
        int index = key % array.length;
        //2.遍历数组中index下表位置所对应的桶
        for(Node cur = array[index]; cur != null; cur = cur.next) {
            if(cur.key == key) {
                return;
            }
        }
        //3.循环结束，桶中不存在此元素，进行尾插法法如桶中
        Node node = new Node(key);
        node.next = array[index];
        array[index] = node;
        this.usedSize++;
    }
    
    public void remove(int key) {
        int index = key % array.length;
        if(array[index] == null) {
            return;
        }
        Node cur = array[index];
        // 要删除的值是改桶的头结点
        if(cur.key == key) {
            array[index] = cur.next;
            this.usedSize--;
            return;
        }
        while(cur.next != null) {
            if(cur.next.key == key) {
                cur.next = cur.next.next;
                this.usedSize--;
                return;
            }
            cur = cur.next;
        }
    }
    
    /** Returns true if this set contains the specified element */
    public boolean contains(int key) {
        int index = key % array.length;
        for(Node cur = array[index]; cur != null; cur = cur.next) {
            if(cur.key == 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);
 */

方法2：也可以直接new一个boolean类型的数组
用时比较快

class MyHashSet {
private boolean[] hashSet;
    /** Initialize your data structure here. */
    public MyHashSet() {
        hashSet = new boolean[1000001];
    }
    
    public void add(int key) {
        hashSet[key] = true;
    }
    
    public void remove(int key) {
        hashSet[key] = false;
    }
    
    /** Returns true if this set contains the specified element */
    public boolean contains(int key) {
        return hashSet[key];
    }
}
/**
 * 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);
 */