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 {
    private final int MAX_LEN = 100000; // the amount of buckets
    private List<Integer>[] set;      // hash set implemented by array

    /** Returns the corresponding bucket index. */
    private int getIndex(int key) {
        return key % MAX_LEN;
    }

    /** Search the key in a specific bucket. Returns -1 if the key does not existed. */
    private int getPos(int key, int index) {
        // Each bucket contains a list.
        List<Integer> temp = set[index];
        if (temp == null) {
            return -1;
        }
        // Iterate all the elements in the bucket to find the target key.
        for (int i = 0; i < temp.size(); ++i) {
            if (temp.get(i) == key) {
                return i;
            }
        }
        return -1;
    }

    /** Initialize your data structure here. */
    public MyHashSet() {
        set = (List<Integer>[])new ArrayList[MAX_LEN];
    }

    public void add(int key) {
        int index = getIndex(key);
        int pos = getPos(key, index);
        if (pos < 0) {
            // Add new key if key does not exist.
            if (set[index] == null) {
                set[index] = new ArrayList<Integer>();
            }
            set[index].add(key);
        }
    }

    public void remove(int key) {
        int index = getIndex(key);
        int pos = getPos(key, index);
        if (pos >= 0) {
            // Remove the key if key exists.
            set[index].remove(pos);
        }
    }

    /** Returns true if this set did not already contain the specified element */
    public boolean contains(int key) {
        int index = getIndex(key);
        int pos = getPos(key, index);
        return pos >= 0;
    }
}

/**
 * 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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