/***********************************************************
 * @Description : 支持动态扩缩容的哈希表
 * @author      : 梁山广(Liang Shan Guang)
 * @date        : 2020/1/5 20:29
 * @email       : liangshanguang2@gmail.com
 ***********************************************************/
package Chapter14HashTable.Section6DynamicHashTable;

import java.util.TreeMap;

public class HashTable<K, V> {

    private static final int upperTol = 10;
    private static final int lowerTol = 2;
    private static final int initCapacity = 7;

    private TreeMap<K, V>[] hashtable;
    private int size;
    private int M;

    public HashTable(int M){
        this.M = M;
        size = 0;
        hashtable = new TreeMap[M];
        for(int i = 0 ; i < M ; i ++) {
            hashtable[i] = new TreeMap<>();
        }
    }

    public HashTable(){
        this(initCapacity);
    }

    private int hash(K key){
        return (key.hashCode() & 0x7fffffff) % M;
    }

    public int getSize(){
        return size;
    }

    public void add(K key, V value){
        TreeMap<K, V> map = hashtable[hash(key)];
        if(map.containsKey(key)) {
            map.put(key, value);
        } else{
            map.put(key, value);
            size ++;
            if(size >= upperTol * M) {
                resize(2 * M);
            }
        }
    }

    public V remove(K key){
        V ret = null;
        TreeMap<K, V> map = hashtable[hash(key)];
        if(map.containsKey(key)){
            ret = map.remove(key);
            size --;

            if(size < lowerTol * M && M / 2 >= initCapacity) {
                resize(M / 2);
            }
        }
        return ret;
    }

    public void set(K key, V value){
        TreeMap<K, V> map = hashtable[hash(key)];
        if(!map.containsKey(key)) {
            throw new IllegalArgumentException(key + " doesn't exist!");
        }

        map.put(key, value);
    }

    public boolean contains(K key){
        return hashtable[hash(key)].containsKey(key);
    }

    public V get(K key){
        return hashtable[hash(key)].get(key);
    }

    private void resize(int newM){
        TreeMap<K, V>[] newHashTable = new TreeMap[newM];
        for(int i = 0 ; i < newM ; i ++) {
            newHashTable[i] = new TreeMap<>();
        }

        int oldM = M;
        this.M = newM;
        for(int i = 0 ; i < oldM ; i ++){
            TreeMap<K, V> map = hashtable[i];
            for(K key: map.keySet()) {
                newHashTable[hash(key)].put(key, map.get(key));
            }
        }

        this.hashtable = newHashTable;
    }
}