706. Design HashMap

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706. Design HashMap

Description

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

Implement the MyHashMap class:

  • MyHashMap() initializes the object with an empty map.
  • void put(int key, int value) inserts a (key, value) pair into the HashMap. If the key already exists in the map, update the corresponding value.
  • int get(int key) returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key.
  • void remove(key) removes the key and its corresponding value if the map contains the mapping for the key.

Example 1:

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Input

["MyHashMap", "put", "put", "get", "get", "put", "get", "remove", "get"]
[[], [1, 1], [2, 2], [1], [3], [2, 1], [2], [2], [2]]
Output

[null, null, null, 1, -1, null, 1, null, -1]

Explanation

MyHashMap myHashMap = new MyHashMap();
myHashMap.put(1, 1); // The map is now [[1,1]]
myHashMap.put(2, 2); // The map is now [[1,1], [2,2]]
myHashMap.get(1);    // return 1, The map is now [[1,1], [2,2]]
myHashMap.get(3);    // return -1 (i.e., not found), The map is now [[1,1], [2,2]]
myHashMap.put(2, 1); // The map is now [[1,1], [2,1]] (i.e., update the existing value)
myHashMap.get(2);    // return 1, The map is now [[1,1], [2,1]]
myHashMap.remove(2); // remove the mapping for 2, The map is now [[1,1]]
myHashMap.get(2);    // return -1 (i.e., not found), The map is now [[1,1]]

Constraints:

  • 0 <= key, value <= 10^6
  • At most 10^4 calls will be made to put, get, and remove.

Hints/Notes

Solution

Language: C++

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class MyHashMap {
private:
    static const int size = 997;
    vector<list<pair<int, int>>> v;
    static int hash(int key) {
        return key % size;
    }

public:
    MyHashMap() : v(size) {

    }

    void put(int key, int value) {
        int h = hash(key);
        for (auto it = v[h].begin(); it != v[h].end(); ++it) {
            if (it->first == key) {
                it->second = value;
                return;
            }
        }
        v[h].push_back({key, value});
    }

    int get(int key) {
        int h = hash(key);
        for (auto it = v[h].begin(); it != v[h].end(); ++it) {
            if (it->first == key) {
                return it->second;
            }
        }
        return -1;
    }

    void remove(int key) {
        int h = hash(key);
        for (auto it = v[h].begin(); it != v[h].end(); ++it) {
            if (it->first == key) {
                v[h].erase(it);
                return;
            }
        }
    }
};

/**
 * 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);
 */