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1 哈希函数设计
- 最简单的方法:模一个素数
2 哈希冲突的处理—— 链地址法(Seperate Chaining)
- Java8 之前,每一个位置对用一个链表;
- Java8 开始,当哈希冲突达到一定程度,每一个位置从链表转成红黑树;
3 实现自定义的哈希表
HashTable
package hashtable;
import java.util.TreeMap;
public class HashTable<K, V> {
private TreeMap<K, V>[] hashtable;
private int M;
private int size;
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(97);
}
private int hash(K key) {
// 负数可以变成正数
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++;
}
}
public V remove(K key) {
TreeMap<K, V> map = hashtable[hash(key)];
V ret = null;
if (map.containsKey(key)) {
ret = map.remove(key);
size--;
}
return ret;
}
public void set(K key, V value) {
TreeMap<K, V> map = hashtable[hash(key)];
if (!map.containsKey(key)) {
throw new IllegalArgumentException(key + "not 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);
}
}