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Design HashMap

Updated: Mar 24, 2021

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.

Solution:

class MyHashMap {
private int[] map;
    /** Initialize your data structure here. */
    public MyHashMap() {
        map = new int[100001];
    }
    
    /** value will always be non-negative. */
    public void put(int key, int value) {
     map[key] = value+1;   
    }
    
    /** Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key */
    public int get(int key) {
        return map[key]-1;
    }
    
    /** Removes the mapping of the specified value key if this map contains a mapping for the key */
    public void remove(int key) {
        map[key]=0;
    }
}

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