text: //23280692718581
  // inputStr = awaglknagawunagwkwagl
  // num = 4
  
  // Constraints
  // 0 <= num <= 26
  
  
  // accepts string of lowercase letters and a number between 0 and 26.
  // returns an array of unique substrings
  // each substring must also only contain unique, non-replicated letters
  function subStringsKDist(inputStr, num) {
    const substrings = [];
    // iterate through inputStr, checking each iteration for unique substring
    for (let i = 0; i <= inputStr.length - num; i += 1) {
      const letters = {}; // contains letters of substring
      let pointer = i;
      let substring = '';
      let currLetter = inputStr[pointer];
      // iterate from i to i + num (the substring length), unless duplicate letter found
      while (!letters[currLetter] && pointer < i + num) {
        substring += currLetter;
        pointer += 1;
        letters[currLetter] = 1;
        currLetter = inputStr[pointer];
      }
      // if there was no duplicate letters, and substring is unique, add to substrings
      if (substring.length === num && !substrings.includes(substring)) {
        substrings.push(substring);
      }
    }
    return substrings;
  }
  