706. Design HashMap

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

To be specific, your design should include these functions:

• put(key, value) : Insert a (key, value) pair into the HashMap. If the value already exists in the HashMap, update the value.

• get(key): Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key.

• remove(key) : Remove the mapping for the value key if this map contains the mapping for the key.

Example:

MyHashMap hashMap = new MyHashMap();
hashMap.put(1, 1);          
hashMap.put(2, 2);         
hashMap.get(1);            // returns 1
hashMap.get(3);            // returns -1 (not found)
hashMap.put(2, 1);          // update the existing value
hashMap.get(2);            // returns 1 
hashMap.remove(2);          // remove the mapping for 2
hashMap.get(2);            // returns -1 (not found) 

Note:

• All keys and 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 HashMap library.

// Using STL list
class MyHashMap {
public:
    /** Initialize your data structure here. */
    MyHashMap() {
        m_data.resize(m_size);
    }
    
    /** value will always be non-negative. */
    void put(int key, int value) {
        auto& list = m_data[key % m_size];
        for (auto& node : list) {
            if (node.first == key) {
                node.second = value;
                return;
            }
        }
        list.emplace_back(key, value);
    }
    
    /** Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key */
    int get(int key) {
        const auto& list = m_data[key % m_size];
        if (list.empty()) return -1;
        for (const auto& node : list) {
            if (node.first == key) return node.second;
        }
        return -1;
    }
    
    /** Removes the mapping of the specified value key if this map contains a mapping for the key */
    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;
            }
        }
    }
private:
    vector<list<pair<int, int> > > m_data;
    size_t m_size = 1000;
};

class MyHashMap {
public:
    class ListNode {
    public:
        int key, val;
        ListNode* next;
        ListNode(int k, int v) : key(k), val(v), next(nullptr) {} 
    };
    
    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;
    }
    
    /** Initialize your data structure here. */
    MyHashMap() : nodes(vector<ListNode*>(1000, nullptr)) {
        
    }
    
    // Destructor
    ~MyHashMap() {
        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;
                }
            }
        }
    }
    
    /** value will always be non-negative. */
    void put(int key, int value) {
        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, value);
        else prev->next->val = value;
    }
    
    /** Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key */
    int get(int key) {
        int i = idx(key);
        if (!nodes[i]) return -1;
        ListNode* prev = find(nodes[i], key);
        return !prev->next ? -1 : prev->next->val;
    }
    
    /** Removes the mapping of the specified value key if this map contains a mapping for the key */
    void remove(int key) {
        int i = idx(key);
        if (!nodes[i]) return;
        ListNode* prev = find(nodes[i], key);
        if (!prev->next) return;
        ListNode* node_to_delete = prev->next;
        prev->next = prev->next->next;
        delete node_to_delete;
        node_to_delete = nullptr;
    }
};

/**
 * Your MyHashMap object will be instantiated and called as such:
 * MyHashMap* obj = new MyHashMap();
 * obj->put(key,value);
 * int param_2 = obj->get(key);
 * obj->remove(key);
 */