Design HashMap

,

Problem

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

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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

My Answer

  • 2차원 배열을 이용해서 값을 저장하자.
  • 첫번째 index가 어떤 Bucket인지를 결정. value의 범위가 0~1000000이기 때문에, value / 1000를 첫번째 index를 구하는 함수로 사용 (getHash).
  • 두번째 index가 Bucket에서 저장될 위치를 결정. value의 범위가 0~1000000이기 때문에, value % 1000를 두번째 index를 구하는 함수로 사용 ( getIndex).
  • add함수에서 파라미터로 넘어온 value에 맞춰서 getHash, getIndex를 구하고, 현재 2차원 배열의 길이가 Hash, Index 보다 작다면 사이즈를 키운다.
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class MyHashMap {
    int[][] values;
    /** Initialize your data structure here. */
    public MyHashMap() {
        values=new int[0][0];
    }
    
    /** value will always be non-negative. */
    public void put(int key, int value) {
        if ( get(key) >= 0 ) {
            int hash = getHash(key);    
            int index = getIndex(key);
            values[hash][index] = value;
            
            return;
        }
            
        int hash = getHash(key);
        if ( values.length <= hash ) {
            int[][] new_v = new int[hash + 1][];
            
            for(int i=0;i<new_v.length;i++) {
                if ( i < values.length) {
                    new_v[i] = new int[values[i].length];
                    System.arraycopy(values[i], 0, new_v[i], 0, values[i].length);    
                } else {
                    new_v[i] = new int[0];
                }                
            }
            values = new_v;
        }
        
        int index = getIndex(key);
        int sub_count = values[hash].length;
        if ( sub_count <= index ) {
            int[] new_sub = new int[index + 1];    
            for(int i=0;i<new_sub.length;i++) {
                int org_value = -1;
                if ( i < sub_count ) {
                    org_value = values[hash][i];
                } 
                
                new_sub[i] = org_value;
            }
            values[hash] = new_sub;
        }
        
        values[hash][index] = value;
    }
    
    /** 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) {
        int hash = getHash(key);
        
        if ( values.length <= hash ) return -1;
        
        int index = getIndex(key);
        if ( values[hash].length <= index ) return -1;
        
        return values[hash][index];
    }
    
    int getHash(int key) {
        return key / 1000;        
    }
    
    int getIndex(int key) {
        return key % 1000;
    }
    
    /** Removes the mapping of the specified value key if this map contains a mapping for the key */
    public void remove(int key) {
        if ( get(key) < 0 ) return;
        
        int hash = getHash(key);
        int index = getIndex(key);
        
        values[hash][index] = -1;
    }
}

/**
 * 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);
 */

참고