[LeetCode] 705. Design HashSet

Problem

esign 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.

Solution

class MyHashSet {
    
    class Bucket {
        ListNode head = new ListNode(-1);
    }
    
    class ListNode {
        int key;
        ListNode next;
        ListNode(int key) {
            this.key = key;
        }
    }
    
    int size = 10000;
    Bucket[] buckets = new Bucket[size];
    
    int hash(int key) {
        return key%size;
    }
    
    ListNode find(Bucket bucket, int key) {
        ListNode head = bucket.head;
        ListNode pre = head;
        while (head != null && head.key != key) {
            pre = head;
            head = head.next;
        }
        return pre;
    }
    
    public void add(int key) {
        int i = hash(key);
        if (buckets[i] == null) buckets[i] = new Bucket();
        ListNode pre = find(buckets[i], key);
        if (pre.next == null) pre.next = new ListNode(key);
    }
    
    public void remove(int key) {
        int i = hash(key);
        if (buckets[i] != null) {
            ListNode pre = find(buckets[i], key);
            if (pre.next != null) pre.next = pre.next.next;
        }
    }
    
    /** Returns true if this set contains the specified element */
    public boolean contains(int key) {
        int i = hash(key);
        if (buckets[i] != null) {
            ListNode pre = find(buckets[i], key);
            return pre.next == null ? false : true;
        }
        return false;
    }
}