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