Design Hashset Problem

Problem

Design a HashSet without using any built-in hash table libraries.

Implement MyHashSet class:

  • void add(key) Inserts the value key into the HashSet.
  • bool contains(key) Returns whether the value key exists in the HashSet or not.
  • void remove(key) Removes the value key in the HashSet. If key does not exist in the HashSet, do nothing.

Examples

Example 1:

Input
["MyHashSet", "add", "add", "contains", "contains", "add", "contains", "remove", "contains"]
[ [], [1], [2], [1], [3], [2], [2], [2], [2] ]
Output
[null, null, null, true, false, null, true, null, false]

Explanation
MyHashSet myHashSet = new MyHashSet();
myHashSet.add(1);      // set = [1]
myHashSet.add(2);      // set = [1, 2]
myHashSet.contains(1); // return True
myHashSet.contains(3); // return False, (not found)
myHashSet.add(2);      // set = [1, 2]
myHashSet.contains(2); // return True
myHashSet.remove(2);   // set = [1]
myHashSet.contains(2); // return False, (already removed)

Constraints

  • 0 <= key <= 10^6
  • At most 10^4 calls will be made to add, remove, and contains.

Solution

Method 1 - Using Simple Array

class MyHashSet {
    private int[] arr;
    /** Initialize your data structure here. */
    public MyHashSet() {
        arr = new int[1000001];
    }
    
    public void add(int key) {
        arr[key] = key + 1;
    }
    
    public void remove(int key) {
        arr[key] = 0; // handle the case key=0
    }
    
    /** Returns true if this set contains the specified element */
    public boolean contains(int key) {
        return (arr[key] != 0);
    }
}