D-2.md

🔮 Question - 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.

🐉 Solution

class MyHashSet {
    int arr[];

    /** Initialize your data structure here. */
    public MyHashSet() {
        arr=new int[1000001];
        Arrays.fill(arr,-1);
    }
    
    public void add(int key) {
        arr[key]=key;
    }
    
    public void remove(int key) {
        arr[key]=-1;
    }
    
    /** Returns true if this set contains the specified element */
    public boolean contains(int key) {
        return arr[key]!=-1;
    }
}

/**
 * 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);
 */