149 lines
4.1 KiB
Java
149 lines
4.1 KiB
Java
/**
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* File: hash_map_chaining.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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import java.util.ArrayList;
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import java.util.List;
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/* 鏈式位址雜湊表 */
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class HashMapChaining {
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int size; // 鍵值對數量
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int capacity; // 雜湊表容量
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double loadThres; // 觸發擴容的負載因子閾值
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int extendRatio; // 擴容倍數
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List<List<Pair>> buckets; // 桶陣列
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/* 建構子 */
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public HashMapChaining() {
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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 ArrayList<>(capacity);
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for (int i = 0; i < capacity; i++) {
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buckets.add(new ArrayList<>());
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}
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}
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/* 雜湊函式 */
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int hashFunc(int key) {
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return key % capacity;
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}
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/* 負載因子 */
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double loadFactor() {
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return (double) size / capacity;
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}
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/* 查詢操作 */
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String get(int key) {
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int index = hashFunc(key);
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List<Pair> bucket = buckets.get(index);
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// 走訪桶，若找到 key ，則返回對應 val
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for (Pair pair : bucket) {
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if (pair.key == key) {
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return pair.val;
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}
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}
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// 若未找到 key ，則返回 null
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return null;
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}
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/* 新增操作 */
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void put(int key, String val) {
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// 當負載因子超過閾值時，執行擴容
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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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List<Pair> bucket = buckets.get(index);
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// 走訪桶，若遇到指定 key ，則更新對應 val 並返回
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for (Pair pair : bucket) {
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if (pair.key == key) {
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pair.val = val;
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return;
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}
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}
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// 若無該 key ，則將鍵值對新增至尾部
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Pair pair = new Pair(key, val);
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bucket.add(pair);
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size++;
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}
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/* 刪除操作 */
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void remove(int key) {
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int index = hashFunc(key);
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List<Pair> bucket = buckets.get(index);
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// 走訪桶，從中刪除鍵值對
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for (Pair pair : bucket) {
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if (pair.key == key) {
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bucket.remove(pair);
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size--;
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break;
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}
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}
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}
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/* 擴容雜湊表 */
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void extend() {
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// 暫存原雜湊表
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List<List<Pair>> bucketsTmp = buckets;
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// 初始化擴容後的新雜湊表
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capacity *= extendRatio;
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buckets = new ArrayList<>(capacity);
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for (int i = 0; i < capacity; i++) {
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buckets.add(new ArrayList<>());
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}
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size = 0;
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// 將鍵值對從原雜湊表搬運至新雜湊表
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for (List<Pair> bucket : bucketsTmp) {
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for (Pair pair : bucket) {
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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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/* 列印雜湊表 */
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void print() {
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for (List<Pair> bucket : buckets) {
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List<String> res = new ArrayList<>();
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for (Pair pair : bucket) {
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res.add(pair.key + " -> " + pair.val);
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}
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System.out.println(res);
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}
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}
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}
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public class hash_map_chaining {
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public static void main(String[] args) {
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/* 初始化雜湊表 */
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HashMapChaining map = new HashMapChaining();
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/* 新增操作 */
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// 在雜湊表中新增鍵值對 (key, value)
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map.put(12836, "小哈");
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map.put(15937, "小囉");
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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, "小鴨");
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System.out.println("\n新增完成後，雜湊表為\nKey -> Value");
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map.print();
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/* 查詢操作 */
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// 向雜湊表中輸入鍵 key ，得到值 value
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String name = map.get(13276);
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System.out.println("\n輸入學號 13276 ，查詢到姓名 " + name);
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/* 刪除操作 */
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// 在雜湊表中刪除鍵值對 (key, value)
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map.remove(12836);
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System.out.println("\n刪除 12836 後，雜湊表為\nKey -> Value");
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map.print();
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}
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}
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