docs(docs): add documentation for Next Greater Element I and Remove Duplicates from Sorted Array II, update redirects

apps/docs/content/(01-linear-structures)/two-pointers/80_remove-duplicates-from-sorted-array-ii.mdx

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+---
+title: '80. Remove Duplicates from Sorted Array II'
+description: Given an integer array nums sorted in non-decreasing order, remove some duplicates in-place such that each unique element appears at most twice. The relative order of the elements should be kept the same
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Two Pointers", slug: "two-pointers" }
+issue: "https://github.com/prdlk/leetcode/issues/48"
+sidebar:
+  label: 'Remove Duplicates from Sorted Array II'
+  badge: 'Medium'
+---
+
+### Example 1:
+- Input: `nums = [1,1,1,2,2,3]`
+- Output: `5, nums = [1,1,2,2,3,_]`
+- Explanation: Your function should return `k = 5`, with the first five elements of `nums` being `1`, `1`, `2`, `2` and `3` respectively. It does not matter what you leave beyond the returned `k` (hence they are underscores).
+
+### Example 2:
+- Input: `nums = [0,0,1,1,1,1,2,3,3]`
+- Output: `7, nums = [0,0,1,1,2,3,3,_,_]`
+- Explanation: Your function should return `k = 7`, with the first seven elements of `nums` being `0`, `0`, `1`, `1`, `2`, `3` and `3` respectively. It does not matter what you leave beyond the returned `k` (hence they are underscores).
+
+### Constraints:
+
+- `1 <= nums.length <= 3 * 10^4`
+- `-10^4 <= nums[i] <= 10^4`
+- `nums` is sorted in non-decreasing order.
+
+## Solution
+
+```py
+class Solution:
+    def removeDuplicates(self, nums: list[int]) -> int:
+        slow = 0
+        for fast in range(len(nums)):
+            if slow < 2 or nums[fast] != nums[slow - 2]:
+                nums[slow] = nums[fast]
+                slow += 1
+        return slow
+```