JavaScript 中的 SET（初学者教程）

// 1. create a new set and use the .add() method to add elements
const myset = new set();
myset.add(10);
myset.add(20);
myset.add(30);

console.log(myset); // output: set { 10, 20, 30 }

// 2. check if the set has a specific element using .has() method
console.log(myset.has(20)); // output: true
console.log(myset.has(40)); // output: false

// 3. delete an element from the set using .delete() method
myset.delete(20);
console.log(myset); // output: set { 10, 30 }

// 4. iterate over the set using .keys() method
// in sets, .keys() and .values() do the same thing
for (const key of myset.keys()) {
  console.log(key);
}
// output:
// 10
// 30

// 5. get the size of the set using .size property
console.log(myset.size); // output: 2

/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function(s) {
    let set = new Set();
    let ans = 0;
    let s_index = 0;
    for (let i = 0; i < s.length; i++) {
        if (!set.has(s[i])) {
            set.add(s[i]);
            ans = Math.max(ans, set.size);
        } else {
            while (s_index < i && set.has(s[i])) {
                set.delete(s[s_index++]);
            }
            set.add(s[i]);
            ans = Math.max(ans, set.size);
        }
    }
    return ans;
};

/* 
Example 1:

Input: s = "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3.
Example 2:

Input: s = "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.
Example 3:

Input: s = "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.
*/