LeetCode [705] Design HashSet

705. Design HashSet

Easy

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.

class MyHashSet {
    ListNode[] nodes = new ListNode[1000000];

    /** Initialize your data structure here. */
    public MyHashSet() {
        
    }
    
    public void add(int key) {
        int i = idx(key);
        if(nodes[i]==null) nodes[i] = new ListNode(-1);
        ListNode prev = findPrev(nodes[i],key);
        if(prev.next==null) prev.next = new ListNode(key);
    }
    
    public void remove(int key) {
        int i = idx(key);
        if(nodes[i]==null) return;
        ListNode prev = findPrev(nodes[i],key);
        if(prev.next!=null) prev.next = prev.next.next;
    }
    
    /** Returns true if this set contains the specified element */
    public boolean contains(int key) {
        int i = idx(key);
        if(nodes[i]==null) return false;
        ListNode prev = findPrev(nodes[i], key);
        return prev.next!=null;
    }
    
    ListNode findPrev(ListNode bucket, int key){
        ListNode p = bucket, prev = p;
        while(p!=null && p.key!=key){
            prev = p;
            p = p.next;
        }
        return prev;
    }
    
    int idx(int key){
        return Integer.hashCode(key)%nodes.length;
    }
    
    class ListNode{
        int key;
        ListNode next;
        ListNode(int k){
            key = k;
        }
    }
}

/**
 * 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);
 */