3.js

/** ------------------------------------------------------------------------------
 * 
 * 3. Longest Substring Without Repeating Characters
 * Topics: Hash Table, Sliding Window
 * https://leetcode.com/problems/longest-substring-without-repeating-characters/description/
 * 
 ------------------------------------------------------------------------------ */
/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function (s) {
  let i = 0
  let res = 0
  const map = new Map()

  for (let j = 0; j < s.length; j++) {
    const index = map.get(s[j])
    if (index !== undefined && index >= i) {
      i = index + 1
    }
    res = Math.max(res, j - i + 1)
    map.set(s[j], j)
  }

  return res
}

/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function (s) {
  let len = s.length
  let left = 0,
    right = 0
  let answer = 0

  const set = new Set()

  while (right < len) {
    if (set.has(s[right])) {
      set.delete(s[left])
      left++
    } else {
      set.add(s[right])
      right++
    }

    answer = Math.max(set.size, answer)
  }

  return answer
}

console.log(lengthOfLongestSubstring("abcabcbb"))