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 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