Map

let myMap = new Map();
let keyObj = {};
let keyFunc = function() {};
let keyString = 'a string';
// 添加键
myMap.set(keyString, "和键'a string'关联的值");
myMap.set(keyObj, "和键keyObj关联的值");
myMap.set(keyFunc, "和键keyFunc关联的值");
myMap.size; // 3
// 读取值
myMap.get(keyString);    // "和键'a string'关联的值"
myMap.get(keyObj);       // "和键keyObj关联的值"
myMap.get(keyFunc);      // "和键keyFunc关联的值"
myMap.get('a string');   // "和键'a string'关联的值"
                         // 因为keyString === 'a string'
myMap.get({});           // undefined, 因为keyObj !== {}
myMap.get(function() {}); // undefined, 因为keyFunc !== function () {}

mp.size;
fruits.delete(apples);
fruits.clear();
fruits.has(apples);
// 若Map中含有键，返回true

set

// 创建新的变量
const a = "a";
const b = "b";
const c = "c";
// 创建 Set
const letters = new Set();
// Add the values to the Set
letters.add(a);
letters.add(b);
letters.add(c);
// 创建新的 Set
const letters = new Set(["a","b","c"]);
typeof letters;      // 返回 object。
letters instanceof Set;  // 返回 true

Set 对象的方法和属性

leetcode 128 最长连续序列

var longestConsecutive = function(nums) {
    const set = new Set(nums);
    let ans = 0;
    for(const num of nums) {
       if(!set.has(num-1)) {
           let count = 1,cur = num;
           while(set.has(cur + 1)) {
               cur++;
               count++;
           }
           ans = Math.max(ans,count);
       }
    }
    return ans;
};