How to use JS to implement a hash table
This time I will show you how to use JS to implement a hash table, and what are the precautions for using JS to implement a hash table. The following is a practical case, let's take a look.
In algorithms, especially in algorithms related to arrays, the use of hash tables can solve problems very well, so this article will record some information about JS implementation of hash tables and give solutions to practical problems. example.Note: What this article writes is not a real hash table, but is similar to the use of hash tables.
Part 1: Related knowledge points
Enumeration of attributes:
var person = {
name: "zzw",
sex: "Male",
age: 21
};
for (var prop in person) {
console.log(prop + " ",person[prop]);
}
Deletion of attributes:
var person = {
name: "zzw",
sex: "Male",
age: 21
};
var ifRemove = delete person.name;
for (var prop in person) {
console.log(prop + " ",person[prop]);
}
console.log(ifRemove);
var x = 1; console.log(delete x);
var person = {
name: "zzw",
sex: "Male",
age: 21
};
console.log("age" in person);
console.log("someOther" in person);Adding attributes:
var person = {
name: "zzw",
sex: "Male",
age: 21
};
person["school"] = "XJTU";
console.log(person);Part 2: Using js to implement a hash table
The following is a hash table obtained through the// 创建构造函数HashTable
function HashTable() {
// 初始化哈希表的记录条数size
var size = 0;
// 创建对象用于接受键值对
var res = {};
// 添加关键字，无返回值
this.add = function (key, value) {
//判断哈希表中是否存在key，若不存在，则size加1，且赋值
if (!this.containKey(key)) {
size++;
}
// 如果之前不存在，赋值； 如果之前存在，覆盖。
res[key] = value;
};
// 删除关键字, 如果哈希表中包含key，并且delete返回true则删除，并使得size减1
this.remove = function (key) {
if (this.containKey(key) && (delete res[key])) {
size--;
}
};
// 哈希表中是否包含key，返回一个布尔值
this.containKey = function (key) {
return (key in res);
};
// 哈希表中是否包含value，返回一个布尔值
this.containValue = function (value) {
// 遍历对象中的属性值，判断是否和给定value相等
for (var prop in res) {
if (res[prop] === value) {
return true;
}
}
return false;
};
// 根据键获取value,如果不存在就返回null
this.getValue = function (key) {
return this.containKey(key) ? res[key] : null;
};
// 获取哈希表中的所有value, 返回一个数组
this.getAllValues = function () {
var values = [];
for (var prop in res) {
values.push(res[prop]);
}
return values;
};
// 根据值获取哈希表中的key，如果不存在就返回null
this.getKey = function (value) {
for (var prop in res) {
if (res[prop] === value) {
return prop;
}
}
// 遍历结束没有return，就返回null
return null;
};
// 获取哈希表中所有的key,返回一个数组
this.getAllKeys = function () {
var keys = [];
for (var prop in res) {
keys.push(prop);
}
return keys;
};
// 获取哈希表中记录的条数，返回一个数值
this.getSize = function () {
return size;
};
// 清空哈希表，无返回值
this.clear = function () {
size = 0;
res = {};
};
}Part 3: Application Example
Problem: Given an integer array (unordered), find two of them numbers such that their sum is a specified value, and returns the subscripts of the two numbers (array subscripts start from 0), assuming that the values of the array elements are different. The implementation is as follows:<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>哈希表的使用</title>
</head>
<body>
<script>
function queryIndex(arr, result) {
var hashTable = new HashTable();
var arrLength = arr.length;
var sub = [];
for (var i = 0; i < arrLength; i++) {
// 扫描一遍，存储下标和值
hashTable.add(i, arr[i]);
}
for (var j = 0; j < arrLength; j++) {
if (hashTable.containValue(result - arr[j]) && result !== 2*arr[j]) {
// 获取两个下标，跳出循环
sub.push(j);
var antherIndex = Number(hashTable.getKey(result - arr[j]));
sub.push(antherIndex);
break;
}
}
if (sub.length !== 0) {
return sub;
} else {
return -1;
}
}
console.log(queryIndex([1,5,7,3,8], 15)); // 2, 4
console.log(queryIndex([8,18,28,12,29,17], 46)); // 2, 4
console.log(queryIndex([8,18,28,12,29,17], 2)); // -1
// 创建构造函数HashTable
function HashTable() {
// 初始化哈希表的记录条数size
var size = 0;
// 创建对象用于接受键值对
var res = {};
// 添加关键字，无返回值
this.add = function (key, value) {
//判断哈希表中是否存在key，若不存在，则size加1，且赋值
if (!this.containKey(key)) {
size++;
}
// 如果之前不存在，赋值； 如果之前存在，覆盖。
res[key] = value;
};
// 删除关键字, 如果哈希表中包含key，并且delete返回true则删除，并使得size减1
this.remove = function (key) {
if (this.containKey(key) && (delete res[key])) {
size--;
}
};
// 哈希表中是否包含key，返回一个布尔值
this.containKey = function (key) {
return (key in res);
};
// 哈希表中是否包含value，返回一个布尔值
this.containValue = function (value) {
// 遍历对象中的属性值，判断是否和给定value相等
for (var prop in res) {
if (res[prop] === value) {
return true;
}
}
return false;
};
// 根据键获取value,如果不存在就返回null
this.getValue = function (key) {
return this.containKey(key) ? res[key] : null;
};
// 获取哈希表中的所有value, 返回一个数组
this.getAllValues = function () {
var values = [];
for (var prop in res) {
values.push(res[prop]);
}
return values;
};
// 根据值获取哈希表中的key，如果不存在就返回null
this.getKey = function (value) {
for (var prop in res) {
if (res[prop] === value) {
return prop;
}
}
// 遍历结束没有return，就返回null
return null;
};
// 获取哈希表中所有的key,返回一个数组
this.getAllKeys = function () {
var keys = [];
for (var prop in res) {
keys.push(prop);
}
return keys;
};
// 获取哈希表中记录的条数，返回一个数值
this.getSize = function () {
return size;
};
// 清空哈希表，无返回值
this.clear = function () {
size = 0;
res = {};
};
}
</script>
</body>
</html>How to use JS to implement the Baidu search box
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