feat(content): add new problem pages, reorganize docs into (problems) subfolders, and update meta display to page

apps/docs/content/(01-linear-structures)/hash-table/(problems)/128_longest-consecutive-sequence.mdx

@@ -0,0 +1,56 @@
+---
+title: '128. Longest Consecutive Sequence'
+description: Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "Union-Find", slug: "union-find" }
+issue: "https://github.com/prdlk/leetcode/issues/34"
+sidebar:
+  label: 'Longest Consecutive Sequence'
+  badge: 'Medium'
+---
+
+::::warning
+You must write an algorithm that runs in O(n) time.
+::::
+
+### Example 1:
+- Input: `nums = [100,4,200,1,3,2]`
+- Output: `4`
+- Explanation: The longest consecutive elements sequence is [1, `2`, `3`, 4]. Therefore its length is `4`.
+
+### Example 2:
+- Input: `nums = [0,3,7,2,5,8,4,6,0,1]`
+- Output: `9`
+
+### Example 3:
+- Input: `nums = [1,0,1,2]`
+- Output: `3`
+
+### Constraints:
+
+- `0 <= nums.length <= 10^5`
+- `-10^9 <= nums[i] <= 10^9`
+
+## Solution
+
+```py
+class Solution:
+    def longestConsecutive(self, nums: list[int]) -> int:
+        seen = set(nums)
+        best = 0
+
+        for n in seen:
+            if n - 1 in seen:
+                continue
+
+            length = 1
+            while length + n in seen:
+                length += 1
+
+            best = max(length, best)
+
+        return best
+```