sort-by-freq-prob-and-is-subsequence-prob.js

/**
 * @param {string} s
 * @return {string}
 */
var frequencySort = function(s) {
  let freqObj = {};
  let bucket = {};
  let output = [];

  for (var i = 0; i < s.length; i++) {
    let ch = s.charAt(i);
    if (!freqObj[ch]) {
      freqObj[ch] = 1;
    } else {
      freqObj[ch] += 1;
    }
  }


  for (let ch in freqObj) {
    let freq = freqObj[ch];
    if (!bucket[freq]) {
      bucket[freq] = [];
    }
    bucket[freq].push(new Array(freq + 1).join(ch));
  }

  for (let i = s.length; i > 0; i--) {
    if(bucket[i]) {
      output.push(...bucket[i]);
    }
  }

  return output.join('');
};

/**
 * @param {string} s
 * @param {string} t
 * @return {boolean}
 */
var isSubsequence = function(s, t) {
  let sIndex = 0;
  let tIndex = 0;

  if (s.length === 0) {
    return true;
  }

  while (tIndex < t.length) {
    if (t[tIndex] === s[sIndex]) {
      sIndex++;
      if (sIndex >= s.length) {
        return true;
      }
    }
    tIndex++;
  }

  return false;
};