Algorithm to find the longest substring without repeating characters

lengthOfLongestSubstring.js

// Given a string "input", find the length of the longest substring without repeating characters.

const lengthOfLongestSubstring = (input = "") => {
  const chars = input.split("");
  let buffer = new Map(); // stores the last index for each encountered character
  let maxLen = 0;

  for (let index = 0; index < chars.length; index++) {
    const char = chars[index];
    if (!buffer.has(char)) {
      buffer.set(char, index);
    } else {
      index = buffer.get(char); // jump back to one after the last index of this character
      buffer.clear();
    }

    maxLen = Math.max(maxLen, buffer.size);
  }

  return maxLen;
};

expect(lengthOfLongestSubstring('9098795672298')).toBe(5) // "87956"
expect(lengthOfLongestSubstring('pwwkew')).toBe(3) // "wke"
expect(lengthOfLongestSubstring('bbbbbb')).toBe(1) // "b"