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hello-algo/codes/javascript/chapter_hashing/hash_map_chaining.js

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/**
* File: hash_map_chaining.js
* Created Time: 2023-08-06
* Author: yuan0221 (yl1452491917@gmail.com)
*/
/* 键值对 Number -> String */
class Pair {
constructor(key, val) {
this.key = key;
this.val = val;
}
}
/* 链式地址哈希表 */
class HashMapChaining {
#size; // 键值对数量
#capacity; // 哈希表容量
#loadThres; // 触发扩容的负载因子阈值
#extendRatio; // 扩容倍数
#buckets; // 桶数组
/* 构造方法 */
constructor() {
this.#size = 0;
this.#capacity = 4;
this.#loadThres = 2.0 / 3.0;
this.#extendRatio = 2;
this.#buckets = new Array(this.#capacity).fill(null).map((x) => []);
}
/* 哈希函数 */
#hashFunc(key) {
return key % this.#capacity;
}
/* 负载因子 */
#loadFactor() {
return this.#size / this.#capacity;
}
/* 查询操作 */
get(key) {
const index = this.#hashFunc(key);
const bucket = this.#buckets[index];
// 遍历桶,若找到 key ,则返回对应 val
for (const pair of bucket) {
if (pair.key === key) {
return pair.val;
}
}
// 若未找到 key ,则返回 null
return null;
}
/* 添加操作 */
put(key, val) {
// 当负载因子超过阈值时,执行扩容
if (this.#loadFactor() > this.#loadThres) {
this.#extend();
}
const index = this.#hashFunc(key);
const bucket = this.#buckets[index];
// 遍历桶,若遇到指定 key ,则更新对应 val 并返回
for (const pair of bucket) {
if (pair.key === key) {
pair.val = val;
return;
}
}
// 若无该 key ,则将键值对添加至尾部
const pair = new Pair(key, val);
bucket.push(pair);
this.#size++;
}
/* 删除操作 */
remove(key) {
const index = this.#hashFunc(key);
let bucket = this.#buckets[index];
// 遍历桶,从中删除键值对
for (let i = 0; i < bucket.length; i++) {
if (bucket[i].key === key) {
bucket.splice(i, 1);
this.#size--;
break;
}
}
}
/* 扩容哈希表 */
#extend() {
// 暂存原哈希表
const bucketsTmp = this.#buckets;
// 初始化扩容后的新哈希表
this.#capacity *= this.#extendRatio;
this.#buckets = new Array(this.#capacity).fill(null).map((x) => []);
this.#size = 0;
// 将键值对从原哈希表搬运至新哈希表
for (const bucket of bucketsTmp) {
for (const pair of bucket) {
this.put(pair.key, pair.val);
}
}
}
/* 打印哈希表 */
print() {
for (const bucket of this.#buckets) {
let res = [];
for (const pair of bucket) {
res.push(pair.key + ' -> ' + pair.val);
}
console.log(res);
}
}
}
/* Driver Code */
/* 初始化哈希表 */
const map = new HashMapChaining();
/* 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');
console.log('\n添加完成后哈希表为\nKey -> Value');
map.print();
/* 查询操作 */
// 向哈希表中输入键 key ,得到值 value
const name = map.get(13276);
console.log('\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(12836);
console.log('\n删除 12836 后,哈希表为\nKey -> Value');
map.print();