Design HashMap LeetCode

 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]]

import java.util.Arrays;

class MyHashMap {

    private int[] map;

    public MyHashMap() {

        map = new int[1000001];     // Step 1: Allocate array of all possible keys (0 to 10^6)

        Arrays.fill(map, -1);         // Step 2: Fill with -1 (means key not present)

    }

    public void put(int key, int value) {

        map[key] = value;             // Step 3: Store value at index = key

    }

    public int get(int key) {

        return map[key];              // Step 4: Return value; if -1, key not found

    }

    public void remove(int key) {

        map[key] = -1;                // Step 5: Remove by resetting to -1

    }

}