LeetCode-in-Java

705. Design HashSet

Easy

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.

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 <= 106
• At most 104 calls will be made to add, remove, and contains.

Solution

public class MyHashSet {

    private final boolean[] arr;

    public MyHashSet() {
        arr = new boolean[1000001];
    }

    public void add(int key) {
        arr[key] = true;
    }

    public void remove(int key) {
        arr[key] = false;
    }

    public boolean contains(int key) {
        return arr[key];
    }
}

/*
 * 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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