散列的实现
// 散列类 - 线性探测法
function HashTable () {
this.table = new Array(137);
this.values = [];
this.simpleHash = simpleHash;
this.betterHash = betterHash;
this.showDistro = showDistro;
this.put = put;
this.get = get;
}
function put (key, data) {
let pos = this.betterHash(key);
// this.table[pos] = data;
if (this.table[pos] === undefined) {
this.table[pos] = key;
this.values[pos] = data;
} else {
while (this.table[pos] !== undefined) {
++pos;
}
this.table[pos] = key;
this.values[pos] = data;
}
}
function get (key) {
// return this.table[this.betterHash(key)];
let hash = -1;
hash = this.betterHash(key);
if (hash > -1) {
for (let i = hash; this.table[hash] !== undefined; ++i) {
if (this.table[hash] === key) {
return this.values[hash];
}
}
}
return undefined;
}
function simpleHash (data) {
let total = 0;
for (let i = 0; i < data.length; ++i) {
total += data.charCodeAt(i);
}
return total % this.table.length;
}
function showDistro () {
let n = 0;
for (let i = 0; i < this.table.length; ++i) {
if (this.table[i] !== undefined) {
console.log(`${i}: ${this.table[i]}`);
}
}
}
function betterHash (string) {
const H = 7;
let total = 0;
for (let i = 0; i < string.length; ++i) {
total += H * total + string.charCodeAt(i);
}
total = total % this.table.length;
if (total < 0) {
total += this.table.length -1;
}
return parseInt(total, 10);
}
练习
使用线性探测法创建一个字典，用来保存单词的定义。该程序需要包含两个部分：第一部分将一组单词和它们的定义存储进散列表；第二部分让用户输入单词，程序给出该单词的定义。
// 字典类
function Dict () {
this.hashTable = new HashTable();
this.save = save;
this.find = find;
}
function save (word, description) {
this.hashTable.put(word, description);
}
function find (word) {
return this.hashTable.get(word);
}
// 示例
let d = new Dict();
d.save('Mazey', 'a strong man.');
d.save('Cherrie', 'a beautiful girl.');
d.save('John', 'unknown.');
console.log(d.find('John')); // unknown.
console.log(d.find('Mazey')); // a strong man.
console.log(d.find('Ada')); // undefined