706. Design HashMap

706. Design HashMap (Easy)

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:

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 <= 106
• At most 104 calls will be made to put, get, and remove.

Companies:
Microsoft, Goldman Sachs, LinkedIn, Amazon, Apple, Twitter, ServiceNow, Adobe

Related Topics:
Array, Hash Table, Linked List, Design, Hash Function

Similar Questions:

• Design HashSet (Easy)
• Design Skiplist (Hard)

Solution 1.

// OJ: https://leetcode.com/problems/design-hashmap/
// Author: github.com/lzl124631x
// Time: O(1)
// Space: O(1)
class MyHashMap {
    const static int N = 1000001;
    int m[N];
public:
    MyHashMap() {
        for (int i = 0; i < N; ++i) m[i] = -1;
    }
    void put(int key, int value) {
        m[key] = value;
    }
    int get(int key) {
        return m[key];
    }
    void remove(int key) {
        m[key] = -1;
    }
};