This article brings you relevant knowledge about javascript, mainly introducing the detailed explanation of JavaScript dictionaries and collections. A collection is composed of a group of unordered and non-repeating elements. We can think of a set as a special kind of array. Its special feature is that it is unordered and non-repeating, which means that we cannot access it through subscripts, and there will be no duplicate elements in the set.
[Related recommendations: javascript video tutorial, web front-end]
When it comes to dictionaries, the first thing that comes to mind is the Xinhua Dictionary. In fact, it is similar to the dictionary in programming. Both There is a characteristic that corresponds to one-to-one (yi yi dui ying), or maps .
Dictionaries are usually stored in **[key, value]** pairs. Because they are stored in the form of key-value pairs, it is more convenient to obtain value# through key
##For example, storing user information:
{
'username': '一碗周',
'age': 18
}Map is added in ES6 to represent a dictionary. The map here is not translated into a map, but a mapping.
The sample code is as follows:
// 创建一个字典
const map = new Map()
// 往字典中存储信息
map.set('username', '一碗周')
map.set('age', 18)
console.log(map) // Map(2) { 'username' => '一碗周', 'age' => 18 }Valid brackets. The main idea of the question is to determine whether the brackets in the given string match. If they match, true will be returned, otherwise false will be returned. .
The problem-solving idea is as follows:
, because of the parentheses They all appear in pairs; . Our original solution:
/**
* @param {string} s
* @return {boolean}
*/
var isValid = function(s) {
if (s.length % 2 !== 0) return false
const stack = []
for(let i = 0; i<s.length; i++) {
const c = s[i] // 记录当前项
if (c === '(' || c === '[' || c==='{') {
stack.push(c)
} else {
const t = stack[stack.length - 1] // 获取栈顶元素
if (
(t === '(' && c === ')') ||
(t === '[' && c === ']') ||
(t === '{' && c === '}')
) {
stack.pop()
} else {
return false
}
}
}
// 如果为0表示全部匹配，有剩余则表示不匹配
return stack.length === 0
};implementation code is as follows:
/**
* @param {string} s
* @return {boolean}
*/
var isValid = function(s) {
// 1. 判断字符串的长度是否为偶数，不为偶数直接返回false，因为括号都是成对出现的；
if (s.length % 2 !== 0) return false
const stack = []
const map = new Map() // 将所有括号的对应关系存储在字典中
map.set('(', ')')
map.set('[', ']')
map.set('{', '}')
for(let i = 0; i<s.length; i++) {
const c = s[i] // 记录当前项
// 判断是否存在 key 也就是左括号，如果存储，将左括号存储在栈中
if (map.has(c)) {
stack.push(c)
} else {
const t = stack[stack.length - 1] // 获取栈顶元素
if (map.get(t) === c) { // 获取最后一个左括号，判断是否与右括号匹配
stack.pop() // 出栈
} else {
return false
}
}
}
// 如果为0表示全部匹配，有剩余则表示不匹配
return stack.length === 0
};if statement.
unordered and non-repeating composed of elements. We can think of a set as a special array. Its special feature is that it is unordered and non-repeating, which means that we cannot access it through subscripts, and there will be no duplication in the set. Element;
Set, in MDN The description is as follows:
Operations in the collectionSet
An object is a collection of values, and you can iterate over its elements in the order of insertion. The elements in the Set will onlyappear once, that is, the elements in the Set are unique.
There are mainly the following scene operations in the collection:
Set object provides us with the corresponding method, The sample code is as follows:
const arr = [1, 2, 3, 2, 3, 4, 5] // 利用set实现去重 const set = new Set(arr) // [1, 2, 3, 4, 5] // 往集合中添加元素 set.add(3) // [1, 2, 3, 4, 5] 添加失败，集合中不允许出现重复元素 set.add(6) // [1, 2, 3, 4, 5, 6] // 判断元素是否在集合中 set.has(2) // true set.has(7) // false // 删除集合中的元素 set.delete(1) // [2, 3, 4, 5, 6] // 清空集合 set.clear()
The encapsulated code is as follows:
// 求两个集合的并集
export function union(setA, setB) {
let _union = new Set(setA)
for (let elem of setB) {
_union.add(elem) // 因为集合中不存在重复元素
}
return _union
}
// 求两个集合的交集
export function intersection(setA, setB) {
let _intersection = new Set()
for (let elem of setB) {
if (setA.has(elem)) {
_intersection.add(elem)
}
}
return _intersection
}
// 求两个集合的差集
export function difference(setA, setB) {
let _difference = new Set(setA)
for (let elem of setB) {
_difference.delete(elem)
}
return _difference
}javascript video tutorial, web front-end】
The above is the detailed content of JavaScript dictionaries and collections (summary sharing). For more information, please follow other related articles on the PHP Chinese website!
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
