length_of_longest_substring.js

function lengthOfLongestSubstring(s) {
  
  if (s.length <= 1)
    return s.length
  
  let lookup = new Map()
  let len = s.length
  let max = 0
  let start = 0
  
  for (let i = 0; i < len; i++) {
    let c = s.charAt(i)
    
    if (lookup.has(c) && lookup.get(c) >= start) {
      start = lookup.get(c) + 1; // Read the logic in the notes above
    }
    
    lookup.set(c, i)
    
    max = Math.max(max, i - start + 1)
  }
  
  return max;
}

console.log(lengthOfLongestSubstring('OBAMACARE')) // 4
console.log(lengthOfLongestSubstring('ABBA')) // 2