docs(docs): add LeetCode problem markdown pages and docs site assets

apps/docs/content/(hash-table)/242-valid-anagram.mdx

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+---
+title: '242. Valid Anagram'
+description: Given two strings s and t, return true if t is an anagram of s, and false otherwise
+sidebar:
+  label: 'Valid Anagram'
+  badge: 'Easy'
+---
+
+<Badge variant="accent">Hash Table</Badge>
+
+::::warning
+What if the inputs contain Unicode characters? How would you adapt your solution to such a case?
+::::
+
+### Example 1:
+- Input: `s = "anagram", t = "nagaram"`
+- Output: `true`
+
+### Example 2:
+- Input: `s = "rat", t = "car"`
+- Output: `false`
+
+### Constraints:
+
+- `1 <= s.length, t.length <= 5 * 10^4`
+- `s` and `t` consist of lowercase English letters.
+
+## Solution
+
+```js
+/**
+ * @param {string} s
+ * @param {string} t
+ * @return {boolean}
+ */
+var isAnagram = function(s, t) {
+  let freq = {};
+  for (let c of s) freq[c] = (freq[c] || 0) + 1;
+  
+  for (let c of t) {
+    if(!freq[c] || freq[c] === 0){
+      return false;
+    }
+    freq[c] = freq[c] - 1;
+  }
+  return true;
+};
+```