705. 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.

class MyHashSet {
public:
    /** Initialize your data structure here. */
    MyHashSet() {
        m_data.resize(m_size);
    }
    
    void add(int key) {
        auto& list = m_data[key % m_size];
        for (auto& node : list) {
            if (node.first == key) return;
        }
        list.emplace_back(key, 1);
    }
    
    void remove(int key) {
        auto& list = m_data[key % m_size];
        for (auto it = list.begin(); it != list.end(); ++it) {
            if (it->first == key) {
                list.erase(it);
                return;
            }
        }
    }
    
    /** Returns true if this set contains the specified element */
    bool contains(int key) {
        const auto& list = m_data[key % m_size];
        for (const auto& node : list) {
            if (node.first == key) return true;
        }
        return false;
    }
private:
    vector<list<pair<int, int> > > m_data;
    int m_size = 1000;
};

class MyHashSet {
public:
    class ListNode {
    public:
        int key, val;
        ListNode* next;
        ListNode(int k, int v) : key(k), val(v), next(nullptr) {} 
    };
    
    /** Initialize your data structure here. */
    MyHashSet() : nodes(vector<ListNode*>(1000, nullptr)) {
        
    }
    
    // Destructor
    ~MyHashSet() {
        for (ListNode*& list : nodes) {
            if (list) {
                ListNode* ptr = list;
                while (ptr) {
                    ListNode* node_to_delete = ptr;
                    ptr = ptr->next;
                    delete node_to_delete;
                    node_to_delete = nullptr;
                }
            }
        }
    }
    
    void add(int key) {
        int i = idx(key);
        if (!nodes[i]) nodes[i] = new ListNode(-1, -1); // dummy node for easier removing operation
        ListNode* prev = find(nodes[i], key);
        if (!prev->next) prev->next = new ListNode(key, 1);
    }
    
    void remove(int key) {
        int i = idx(key);
        if (!nodes[i]) return;
        ListNode* prev = find(nodes[i], key);
        if (prev->next) {
            ListNode* node_to_delete = prev->next;
            prev->next = prev->next->next;
            delete node_to_delete;
            node_to_delete = nullptr;
        }
    }
    
    /** Returns true if this set contains the specified element */
    bool contains(int key) {
        int i = idx(key);
        if (!nodes[i]) return false;
        ListNode* prev = find(nodes[i], key);
        if (!prev->next) return false;
        else return true;
    }
private:
    vector<ListNode*> nodes;
    int idx(int key) {
        return key % nodes.size();
    }
    // Returns the previous node of the target key node in the ListNode bucket
    ListNode* find(ListNode* bucket, int key) {
        ListNode* cur = bucket, *prev = nullptr;
        while (cur && cur->key != key) {
            prev = cur;
            cur = cur->next;
        }
        return prev;
    }
};