docs(docs): migrate to array based folder structure

docs/hash-table/451.mdx

@@ -0,0 +1,49 @@
+---
+title: LC-451
+description: Sort Characters By Frequency
+---
+
+## Examples
+
+| Input      | Output   |
+| ---------- | -------- |
+| `"tree"`   | `"eert"` |
+| `"cccaaa"` | `"aaaccc"` |
+| `"Aabb"`   | `"bbAa"` |
+
+## Hints
+
+<Accordions type="single">
+  <Accordion title="Constraints">
+    Constraints:
+     • `1 <= s.length <= 5 * 10^5`
+     • `s` consists of uppercase and lowercase English letters and digits.
+  </Accordion>
+  <Accordion title="Problem Statement">
+    Given a string `s`, sort it in decreasing order based on the frequency of the characters.
+    The frequency of a character is the number of times it appears in the string.
+    Return the sorted string. If there are multiple answers, return any of them.
+  </Accordion>
+</Accordions>
+
+## Solution
+
+```js
+/**
+ * @param {string} s
+ * @return {string}
+ */
+
+var frequencySort = function (s) {
+  // Default for Hammer
+  const freq = {};
+  for (let c of s) freq[c] = (freq[c] || 0) + 1;
+
+  // Problem Specific
+  // Sort characters by descending frequency; same chars stay grouped
+  return s
+    .split("")
+    .sort((a, b) => freq[b] - freq[a] || a.localeCompare(b))
+    .join("");
+};
+```