javascript数据结构6-字典散列集合

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6.1 字典

字典是一种以键- 值对形式存储数据的数据结构，就像电话号码簿里的名字和电话号码一

<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>字典sample</title></head><body><script>    function Dictionary(){       this.add = add;       this.datastore = new Array();       this.find = find;       this.remove = remove;       this.showAll = showAll;       this.count = count;       this.clear = clear;    }    function add(key, value) {       this.datastore[key] = value;    }    function find(key) {       return this.datastore[key];    }    function remove(key) {       delete this.datastore[key];    }    function showAll() {    if(this.datastore!=null){       var datakeys=Array.prototype.slice.call(Object.keys(this.datastore));       for (var key in datakeys) {          document.write(datakeys[key] + " -> " + this.datastore[datakeys[key]]+" ");          // console.log(Object.keys(this.datastore));          console.log(key);       }     }else{        document.write("字典为空");     }    }    function count() {       var n = 0;       for  (var key in Object.keys(this.datastore)) {          ++n;       }       return n;    }    function clear() {       // for  (var key in Object.keys(this.datastore)) {       //    delete this.datastore[key];       // }        delete this.datastore;    }    //测试    var dic=new Dictionary();    dic.add("123","R");    dic.add("456","Python");    dic.add("789","JavaScipt");    document.write("</br>**************字典数目**************</br>");    var n=dic.count();    document.write(n);    document.write("</br>**************全部显示**************</br>");    dic.showAll();    document.write("</br>**************删除123--->R*************</br>");    dic.remove("123");    dic.showAll();    document.write("</br>**************清除**************</br>");    dic.clear();    dic.showAll();</script></body></html>

6.2 散列（HashTable）

它通过把关键码值映射到表中一个位置来访问记录，以加快查找的速度
使用：MD5 和 SHA-1 可以说是目前应用最广泛的Hash算法
java中已经实现
这里写图片描述

<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>HashTable散列表</title></head><body><script>    function HashTable() {       this.table = new Array(137); //为了避免碰撞，首先要确保散列表中用来存储数据的数组其大小是个质数。这一点很关键，这和计算散列值时使用的取余运算有关。       this.simpleHash = simpleHash;   //简单的散列表       this.betterHash = betterHash;   //更好的HashTable，避免碰撞       this.showDistro = showDistro;       this.put = put;       //this.get = get;    }    function put(data) {       var pos = this.simpleHash(data);       this.table[pos] = data;    }    function simpleHash(data) {       var total = 0;       for (var i = 0; i < data.length; ++i) {          total += data.charCodeAt(i);       }       document.write("Hash value: " + data + " -> " + total+"<br/>");       return total % this.table.length;    }    function showDistro() {       var n = 0;       for (var i = 0; i < this.table.length; ++i) {          if (this.table[i] != undefined) {             document.write(i + ": " + this.table[i]+"<br/>");          }       }    }    function betterHash(string) {       const H = 31;  //较小的质数  书上37不行        var total = 0;       for (var 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);    }    var someNames = ["David", "Jennifer", "Donnie", "Raymond",                 "Cynthia", "Mike", "Clayton", "Danny", "Jonathan"];    var hTable = new HashTable();    for (var i = 0; i < someNames.length; ++i) {         hTable.put(someNames[i]);    }    hTable.showDistro();</script></body></html>

这里写图片描述
这就是碰撞，为避免碰撞，使用betterHash
修改：

function put(data) {       // var pos = this.simpleHash(data);       var pos = this.betterHash(data);       this.table[pos] = data;    }

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javascript数据结构6-字典 散列 集合

6.1 字典

6.2 散列（HashTable）

javascript数据结构6-字典散列集合