Design HashSet | LeetCode Problems And Solution

This post explains the LeetCode problem Design HashSet step by step: the problem statement, input and output format, constraints, a sample test case and a working solution in Java that you can study and run.

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

Design HashSet Solution

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.

Design HashSet Solution in Java

class MyHashSet {
    /** Initialize your data structure here. */
    class Node {
        int val;
        Node next;
        public Node(int val) {
            this.val = val;
        }
    }
    private int size;
    private Node[] array;
    /** Initialize your data structure here. */
    public MyHashSet() {
        this.size = 100;
        this.array = new Node[100];
    }
    public void add(int key) {
        int index = key % this.size;
        if(this.array[index] == null) {
            this.array[index] = new Node(key);
            return;
        } else {
            Node p = this.array[index];
            while(p != null && p.val != key) 
                p = p.next;

            if(p != null) 
                return;

            Node newHead = new Node(key);
            newHead.next = this.array[index];
            this.array[index] = newHead;
        }
    }

    public void remove(int key) {
        int index = key % this.size;
        if(this.array[index] == null) {
            return;
        } else {
            Node p = this.array[index];

            if(p.val == key) {
                this.array[index] = p.next;
                return;
            }
            while(p.next != null && p.next.val != key)
                p = p.next;
            if(p.next == null)
                return;
            p.next = p.next.next;
        }
    }
    /** Returns true if this set contains the specified element */
    public boolean contains(int key) {
        int index = key % this.size;
        if(this.array[index] == null)
            return false;
        Node p = this.array[index];
        while(p != null && p.val != key)
            p = p.next;
        return p != null;
    }
}
/**
 * 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);
 */

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