705. Design HashSet (Easy)

https://leetcode.com/problems/design-hashset/

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.

Solutions

class MyHashSet {
    private List<Integer> list = null;

    public MyHashSet() {
        list = new ArrayList<>();
    }

    public void add(int key) {
        if (contains(key)) {
            return;
        }

        list.add(key);
    }

    public void remove(Object key) {
        list.remove(key);
    }

    public boolean contains(int key) {
        return list.contains(key);
    }
}

Incorrect Solutions

References