拉链法哈希表
拉链法哈希表
2019-07-03 13:31:32
import java.io.ObjectInputStream; import java.util.ArrayList; import java.util.Iterator; /** * @ClassName SeparateChainHashST * @Author wangyudi * @Date 2019/7/2 22:25 * @Version 1.0 * @Description 拉链法散列表（哈希表） */ public class SeparateChainHashST<Key, Value> { private int m;//数组大小 private int n;//键值对数量 private Chain<Key, Value>[] st;//存放链表的数组 private ArrayList<Key> list; //用于迭代获取键的集合 public SeparateChainHashST() { this(997); } public SeparateChainHashST(int m) { this.m = m; st = (Chain<Key, Value>[]) new Chain[m]; //实例化数组 for (int i = 0; i < m; i++) { st[i] = new Chain<Key, Value>(); //数组每个元素都指向一个空链表 } this.n = 0; } public int getSize(){ return m; } /** * 为了保证每条链的大小保持在2~8，调整数组的大小到size * 将源哈希表中所有键值对插入到新哈希表中；然后将新哈希表中的成员给源哈希表 * @param size */ private void resize(int size){ SeparateChainHashST<Key, Value> keyValueSeparateChainHashST = new SeparateChainHashST<>(size); for(int i=0;i<m;i++){ for(Object[] o : st[i]){ keyValueSeparateChainHashST.put((Key)o[0],(Value)o[1]); } } this.m = keyValueSeparateChainHashST.m; this.st = keyValueSeparateChainHashST.st; } /** * 返回可迭代的对象 * * @return */ public Iterable<Key> keys() { list = new ArrayList<>(); for (int i = 0; i < m; i++) { for (Object[] o : st[i]) { list.add((Key)o[0]); } } return list; } /** * 根据键的hashcode，计算每个键的索引值 * * @param key * @return */ private int hash(Key key) { return (key.hashCode() & 0x7FFFFFFF) % m; } /** * 向哈希表中放入一个键值对，如果存在相同的键则更新该键的值 * * @param key * @param value */ public void put(Key key, Value value) { if(n>8*m){ resize(2*m); } int i = hash(key);//找到键所在的数组索引 st[i].put(key, value);//将插入键值对的问题交给链表 n++; } /** * 根据键，从哈希表获取相应的值；没有该键则返回null */ public Value get(Key key) { int i = hash(key); return st[i].get(key); } /** * 从哈希表删除键值对，并返回被删除键的值。 * * @param key * @return */ public void delete(Key key) { int i = hash(key); if(st[i].delete(key)){ n--; } if(n>0&&n<=2*m){ resize(m/2); } } } /** * 链表类 * * @param <Key> * @param <Value> */ class Chain<Key, Value> implements Iterable<Object[]> { private Node first; private class Node { Key key; Value value; Node next; public Node(Key key, Value value, Node next) { this.key = key; this.value = value; this.next = next; } } public Value get(Key key) { for (Node i = first; i != null; i = i.next) { if (i.key == key) { return i.value; } } return null; } public void put(Key key, Value value) { for (Node i = first; i != null; i = i.next) { if (i.key == key) { i.value = value; return; //找到相同的键 } } first = new Node(key, value, first);//在头部加入键值队 } /** * 删除单向链表中的某一个结点 * * @param key * @return */ public boolean delete(Key key) { // if (first == null) { // return false; // } // if (first.key == key) { //判断首结点 // first = first.next; // return true; // } Node f = null; //保存前一结点的信息 Node b = first; while (b != null && b.key != key) { f = b; b = b.next; } if (b != null) { //找到要删除的对象 if(f==null){ first=b.next; //特殊处理 }else { f.next = b.next; } b.next = null; b = null; return true; } return false; } @Override public Iterator<Object[]> iterator() { return new Iterator() { Node i = first; @Override public boolean hasNext() { if (i != null) return true; return false; } @Override public Object[] next() { Key tempkey = i.key; Value tempValue = i.value; Object[] info = new Object[]{(Object)tempkey,(Object)tempValue}; i = i.next; return info; } }; } // public Iterator<Node> nodeIterator(){ // return new Iterator<Node>() { // Node i = first; // @Override // public boolean hasNext() { // if(i!=null)return true; // return false; // } // // @Override // public Node next() { // Node temp = i; // i = i.next; // return temp; // } // }; // } }
public class TestCase { public static void main(String[] args) { SeparateChainHashST<Integer, String> separateChainHashST = new SeparateChainHashST<>(100); separateChainHashST.put(12,"12.."); separateChainHashST.put(2,"2.."); separateChainHashST.put(34,"34.."); separateChainHashST.put(17,"17.."); separateChainHashST.put(55,"55.."); separateChainHashST.put(214,"214.."); separateChainHashST.put(12,"12.."); separateChainHashST.put(2,"2.."); separateChainHashST.put(34,"34.."); separateChainHashST.put(17,"17.."); separateChainHashST.put(55,"55.."); separateChainHashST.put(214,"214.."); for(Integer i : separateChainHashST.keys()){ System.out.println(i); } System.out.println("==============================================="); separateChainHashST.delete(34); for(Integer i : separateChainHashST.keys()){ System.out.println(i); } System.out.println("==============================================="); System.out.println(separateChainHashST.get(55)); System.out.println("==============================================="); System.out.println(separateChainHashST.getSize()); } } //结果 2 12 214 214 17 34 55 =============================================== 2 55 12 214 214 17 =============================================== 55.. =============================================== 50
