集合是由一组无序且唯一的项组成的：
集合可以进行 并集、交集、差集、子集操作。
集合的代码实现：
function Set() {
var items = {};
this.add = function(value) {
if(!this.has(value)) {
items[value] = value;
return true;
}else {
return false;
}
}
this.remove = function(value) {
if(this.has(value)) {
delete items[value];
return true;
}else {
return false;
}
}
this.has = function(value) {
return value in items;
}
this.clear = function() {
this.items = {};
}
this.size = function() {
return Object.keys(items).length;
}
this.values = function() {
var keys = [];
for(let key in items) {
keys.push(key);
}
return keys;
}
this.union = function(otherSet) {
var unionSet = new Set();
let values = this.values();
for(let i=0;i<values.length;i++) {
unionSet.add(values[i]);
}
values = otherSet.values();
for(let i=0; i< values.length; i++) {
unionSet.add(values[i]);
}
return unionSet;
}
this.intersection = function(otherSet) {
var intersection = new Set();
let values = this.values();
for(let i=0; i< values.length; i++) {
if(otherSet.has(values[i])) {
intersection.add(values[i]);
}
}
return intersection;
}
this.difference = function(otherSet) {
const difference = new Set();
let values = this.values();
for(let i=0; i< values.length; i++) {
if(!otherSet.has(values[i])) {
difference.add(values[i]);
}
}
return difference;
}
this.subset = function(otherSet) {
if(this.size() > otherSet.size()) {
return false;
}else{
const values = this.values();
for(let i=0; i< values.length; i++) {
if(!otherSet.has(values[i])) {
return false;
}
}
return true;
}
}
}
const set = new Set();
set.add("aa");
set.add("aa");
set.add("bb");
set.add("ee");
console.log(set.values()); // ['aa', 'bb', 'ee']
console.log(set.size()); // 2
console.log(set.remove('dd')); // false
set.remove("aa");
console.log(set.values()); // ['bb, 'ee']
const set1 = new Set();
set1.add("bb");
set1.add("ff");
set1.add("gg");
console.log(set.union(set1).values()); // [ 'bb', 'ee', 'ff', 'gg' ]
console.log(set.intersection(set1).values()); // [ 'bb' ]
console.log(set.difference(set1).values()); // ['ee']
console.log(set.subset(set1)); // false
