hello-algo/codes/java/chapter_hashing/hash_map_open_addressing.java

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/**
* File: hash_map_open_addressing.java
* Created Time: 2023-06-13
* Author: Krahets (krahets@163.com)
*/
package chapter_hashing;
/* 键值对 */
class Pair {
public int key;
public String val;
public Pair(int key, String val) {
this.key = key;
this.val = val;
}
}
/* 开放寻址哈希表 */
class HashMapOpenAddressing {
private int size; // 键值对数量
private int capacity; // 哈希表容量
private double loadThres; // 触发扩容的负载因子阈值
private int extendRatio; // 扩容倍数
private Pair[] buckets; // 桶数组
private Pair removed; // 删除标记
/* 构造方法 */
public HashMapOpenAddressing() {
size = 0;
capacity = 4;
loadThres = 2.0 / 3.0;
extendRatio = 2;
buckets = new Pair[capacity];
removed = new Pair(-1, "-1");
}
/* 哈希函数 */
public int hashFunc(int key) {
return key % capacity;
}
/* 负载因子 */
public double loadFactor() {
return (double) size / capacity;
}
/* 查询操作 */
public String get(int key) {
int index = hashFunc(key);
// 线性探测,从 index 开始向后遍历
for (int i = 0; i < capacity; i++) {
// 计算桶索引,越过尾部返回头部
int j = (index + i) % capacity;
// 若遇到空桶,说明无此 key ,则返回 null
if (buckets[j] == null)
return null;
// 若遇到指定 key ,则返回对应 val
if (buckets[j].key == key && buckets[j] != removed)
return buckets[j].val;
}
return null;
}
/* 添加操作 */
public void put(int key, String val) {
// 当负载因子超过阈值时,执行扩容
if (loadFactor() > loadThres) {
extend();
}
int index = hashFunc(key);
// 线性探测,从 index 开始向后遍历
for (int i = 0; i < capacity; i++) {
// 计算桶索引,越过尾部返回头部
int j = (index + i) % capacity;
// 若遇到空桶、或带有删除标记的桶,则将键值对放入该桶
if (buckets[j] == null || buckets[j] == removed) {
buckets[j] = new Pair(key, val);
size += 1;
return;
}
// 若遇到指定 key ,则更新对应 val
if (buckets[j].key == key) {
buckets[j].val = val;
return;
}
}
}
/* 删除操作 */
public void remove(int key) {
int index = hashFunc(key);
// 线性探测,从 index 开始向后遍历
for (int i = 0; i < capacity; i++) {
// 计算桶索引,越过尾部返回头部
int j = (index + i) % capacity;
// 若遇到空桶,说明无此 key ,则直接返回
if (buckets[j] == null) {
return;
}
// 若遇到指定 key ,则标记删除并返回
if (buckets[j].key == key) {
buckets[j] = removed;
size -= 1;
return;
}
}
}
/* 扩容哈希表 */
public void extend() {
// 暂存原哈希表
Pair[] bucketsTmp = buckets;
// 初始化扩容后的新哈希表
capacity *= extendRatio;
buckets = new Pair[capacity];
size = 0;
// 将键值对从原哈希表搬运至新哈希表
for (Pair pair : bucketsTmp) {
if (pair != null && pair != removed) {
put(pair.key, pair.val);
}
}
}
/* 打印哈希表 */
public void print() {
for (Pair pair : buckets) {
if (pair != null) {
System.out.println(pair.key + " -> " + pair.val);
} else {
System.out.println("null");
}
}
}
}
public class hash_map_open_addressing {
public static void main(String[] args) {
/* 初始化哈希表 */
HashMapOpenAddressing map = new HashMapOpenAddressing();
/* 添加操作 */
// 在哈希表中添加键值对 (key, value)
map.put(12836, "小哈");
map.put(15937, "小啰");
map.put(16750, "小算");
map.put(13276, "小法");
map.put(10583, "小鸭");
System.out.println("\n添加完成后哈希表为\nKey -> Value");
map.print();
/* 查询操作 */
// 向哈希表输入键 key ,得到值 value
String name = map.get(13276);
System.out.println("\n输入学号 13276 ,查询到姓名 " + name);
/* 删除操作 */
// 在哈希表中删除键值对 (key, value)
map.remove(16750);
System.out.println("\n删除 16750 后,哈希表为\nKey -> Value");
map.print();
}
}