README_EN.md

705. Design HashSet

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Description

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.

 

Follow up: Could you solve the problem without using the built-in HashSet library?

Solutions

Python3

class MyHashSet:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.data = [False] * 1000001

    def add(self, key: int) -> None:
        self.data[key] = True

    def remove(self, key: int) -> None:
        self.data[key] = False

    def contains(self, key: int) -> bool:
        """
        Returns true if this set contains the specified element
        """
        return self.data[key]



# Your MyHashSet object will be instantiated and called as such:
# obj = MyHashSet()
# obj.add(key)
# obj.remove(key)
# param_3 = obj.contains(key)

Java

class MyHashSet {

    private boolean[] data;

    /** Initialize your data structure here. */
    public MyHashSet() {
        data = new boolean[1000001];
    }

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

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

    /** Returns true if this set contains the specified element */
    public boolean contains(int key) {
        return data[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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