0791-custom-sort-string.js

/**
 * Custom Sort String
 * Time Complexity: O(S_LEN + T_LEN)
 * Space Complexity: O(T_LEN)
 */
var customSortString = function (sOrderString, tSourceString) {
  const characterFrequencies = new Array(26).fill(0);
  const alphaCodeOffset = "a".charCodeAt(0);

  let tIndex = 0;
  const tSourceLength = tSourceString.length;
  while (tIndex < tSourceLength) {
    const currentTCharCode = tSourceString.charCodeAt(tIndex);
    const frequencyIndex = currentTCharCode - alphaCodeOffset;
    characterFrequencies[frequencyIndex]++;
    tIndex++;
  }

  const resultArray = [];
  let sIndex = 0;
  const sOrderLength = sOrderString.length;
  while (sIndex < sOrderLength) {
    const sCurrentCharCode = sOrderString.charCodeAt(sIndex);
    const sFrequencyIndex = sCurrentCharCode - alphaCodeOffset;
    let repetitionCount = characterFrequencies[sFrequencyIndex];
    while (repetitionCount > 0) {
      resultArray.push(String.fromCharCode(sCurrentCharCode));
      repetitionCount--;
    }
    characterFrequencies[sFrequencyIndex] = 0;
    sIndex++;
  }

  let alphaIndex = 0;
  const alphabetRange = 26;
  while (alphaIndex < alphabetRange) {
    const remainingCharAscii = alphaIndex + alphaCodeOffset;
    let remainingCharCount = characterFrequencies[alphaIndex];
    while (remainingCharCount > 0) {
      resultArray.push(String.fromCharCode(remainingCharAscii));
      remainingCharCount--;
    }
    alphaIndex++;
  }

  return resultArray.join("");
};