refactor(Hash Table): optimize character frequency sorting implementation

work/Baton-1/Medium/Hash Table/451.sort-characters-by-frequency.js

@@ -52,5 +52,11 @@
  * @return {string}
  */
 var frequencySort = function (s) {
+  const freq = {};
+  for (let c of s) freq[c] = (freq[c] || 0) + 1;
 
+  return s
+    .split("")
+    .sort((a, b) => freq[b] - freq[a] || a.localeCompare(b))
+    .join("");
 };