longest-substring.js

/**
 *
 * Given a string, find the length of the longest substring without repeating characters.
 *
 * Input: "abcabcbb"
 * Output: 3
 * Explanation: The answer is "abc", with the length of 3.
 *
 * Input: "bbbbb"
 * Output: 1
 * Explanation: The answer is "b", with the length of 1.
 *
 * Input: "pwwkew"
 * Output: 3
 * Explanation: The answer is "wke", with the length of 3.
 * Note that the answer must be a substring, "pwke" is a subsequence and not a substring.
 *
 * */

var findLargestSubstring = input => {
  var chars = input.split("");
  var curr_char;
  var str = "";
  var longest_string = "";
  var hash = {};
  for (var i = 0; i < chars.length; i++) {
    curr_char = chars[i];
    if (!hash[chars[i]]) {
      str += curr_char;
      hash[chars[i]] = { index: i };
    } else {
      if (longest_string.length <= str.length) {
        longest_string = str;
      }
      var prev_dupeIndex = hash[curr_char].index;
      var str_FromPrevDupe = input.substring(prev_dupeIndex + 1, i);
      str = str_FromPrevDupe + curr_char;
      hash = {};
      for (var j = prev_dupeIndex + 1; j <= i; j++) {
        hash[input.charAt(j)] = { index: j };
      }
    }
  }
  return longest_string.length > str.length ? longest_string : str;
};