JavaScript实现没有解决冲突的哈希表

散列算法的作用是尽可能快地在数据结构中找到一个值。

散列函数的作用是给定一个键值，然后返回值在表中的地址。

class ValuePair {                       //用于存放一对键值对
    constructor(key, value) {
        this.key = key;
        this.value = value;
    }
    toString() {
        return `[#${this.key}:${this.value}]`;
    }
}

class HashTable {
    constructor() {
        this.table = {};
    }
    toStrFn(str) {
        if (str === null) {
            return 'null';
        } else if (str === undefined) {
            return 'undefined';
        } else {
            return str.toString();
        }
    }
    loseloseHashTable(key) {    //散列函数
        if (typeof key === 'number') {  //key如果是数值直接返回
            return key;
        }
        let hash = 0;  //用来储存每个字符的ASCII码之和
        const tableKey = this.toStrFn(key);
        for (let i = 0; i < tableKey.length; i++) {
            hash += tableKey.charCodeAt(i);
        }
        return hash % 37;   //为了得到一个比较小的值
    }
    hashCode(key) {
        return this.loseloseHashTable(key);
    }

    put(key, value) {
        if (key == null || value == null) {   //检验key和value是否合法
            return false;
        }
        const position = this.hashCode(key);
        this.table[position] = new ValuePair(key, value);  //为了信息备份将key保存下来
        return true;
    }
    get(key) {
        let valuePair = this.table[this.hashCode(key)];
        return valuePair == null ? undefined : valuePair.value;
    }
    remove(key) {
        if (this.table[this.hashCode(key)] != null) {
            delete this.table[this.hashCode(key)];
            return true;
        }
        return false;
    }
    size() {
        return Object.keys(this.table).length;
    }
    isEmpty() {
        return this.size() === 0;
    }
    toString() {
        if (this.isEmpty()) {
            return "";
        }
        let keys = Object.keys(this.table);
        let objString = `{${keys[0]}=>${this.table[keys[0]]}}`;
        for (let i = 1; i < keys.length; i++) {
            objString = `${objString},{${keys[i]}=>${this.table[keys[i]]}}`;
        }
        return objString;
    }





}
//测试用例

const hash = new HashTable();

console.log(hash.hashCode('Gandalf') + ' - Gandalf');
console.log(hash.hashCode('John') + ' - John');
console.log(hash.hashCode('Tyrion') + ' - Tyrion');

console.log(' ');

console.log(hash.hashCode('Ygritte') + ' - Ygritte');
console.log(hash.hashCode('Jonathan') + ' - Jonathan');
console.log(hash.hashCode('Jamie') + ' - Jamie');
console.log(hash.hashCode('Jack') + ' - Jack');
console.log(hash.hashCode('Jasmine') + ' - Jasmine');
console.log(hash.hashCode('Jake') + ' - Jake');
console.log(hash.hashCode('Nathan') + ' - Nathan');
console.log(hash.hashCode('Athelstan') + ' - Athelstan');
console.log(hash.hashCode('Sue') + ' - Sue');
console.log(hash.hashCode('Aethelwulf') + ' - Aethelwulf');
console.log(hash.hashCode('Sargeras') + ' - Sargeras');

hash.put('Ygritte', 'ygritte@email.com');
hash.put('Jonathan', 'jonathan@email.com');
hash.put('Jamie', 'jamie@email.com');
hash.put('Jack', 'jack@email.com');
hash.put('Jasmine', 'jasmine@email.com');
hash.put('Jake', 'jake@email.com');
hash.put('Nathan', 'nathan@email.com');
hash.put('Athelstan', 'athelstan@email.com');
hash.put('Sue', 'sue@email.com');
hash.put('Aethelwulf', 'aethelwulf@email.com');
hash.put('Sargeras', 'sargeras@email.com');

console.log('**** Printing Hash **** ');

console.log(hash.toString());
// {4 => [#Ygritte: ygritte@email.com]},{5 => [#Aethelwulf: aethelwulf@email.com]},{7 => [#Athelstan: athelstan@email.com]},{8 => [#Jasmine: jasmine@email.com]},{9 => [#Jake: jake@email.com]},{10 => [#Sargeras: sargeras@email.com]}

console.log('**** Get **** ');

console.log(hash.get('Ygritte')); // ygritte@email.com
console.log(hash.get('Loiane')); // jasmine@email.com

console.log('**** Remove **** ');

hash.remove('Ygritte');
console.log(hash.get('Ygritte')); // undefined

console.log(hash.toString());
// {5 => [#Aethelwulf: aethelwulf@email.com]},{7 => [#Athelstan: athelstan@email.com]},{8 => [#Jasmine: jasmine@email.com]},{9 => [#Jake: jake@email.com]},{10 => [#Sargeras: sargeras@email.com]}