3. Longest Substring Without Repeating Characters

var lengthOfLongestSubstring = function(s) {
    let max = 0
    let left = 0
    const set = new Set()
    for(let r=0; r<s.length; r++){
        while(set.has(s[r])){
            set.delete(s[left])
            left++;
        }
        set.add(s[r])
        max = Math.max(max, r - left +1)
    }
    return max
};