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

apps/docs/content/(01-linear-structures)/monotonic-stack/496_next-greater-element-i.mdx

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+---
+title: '496. Next Greater Element I'
+description: The next greater element of some element x in an array is the first greater element that is to the right of x in the same array
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "Stack", slug: "stack" }
+  - { name: "Monotonic Stack", slug: "monotonic-stack" }
+issue: "https://github.com/prdlk/leetcode/issues/74"
+sidebar:
+  label: 'Next Greater Element I'
+  badge: 'Easy'
+---
+
+::::warning
+Could you find an O(nums1.length + nums2.length) solution?
+::::
+
+### Example 1:
+- Input: `nums1 = [4,1,2], nums2 = [1,3,4,2]`
+- Output: `[-1,3,-1]`
+- Explanation:
+  - The next greater element for each value of `nums1` is as follows:
+  - `4` is underlined in `nums2 = [1,3,4,2]`. There is no next greater element, so the answer is `-1`.
+  - `1` is underlined in `nums2 = [1,3,4,2]`. The next greater element is `3`.
+  - `2` is underlined in `nums2 = [1,3,4,2]`. There is no next greater element, so the answer is `-1`.
+
+### Example 2:
+- Input: `nums1 = [2,4], nums2 = [1,2,3,4]`
+- Output: `[3,-1]`
+- Explanation:
+  - The next greater element for each value of `nums1` is as follows:
+  - `2` is underlined in `nums2 = [1,2,3,4]`. The next greater element is `3`.
+  - `4` is underlined in `nums2 = [1,2,3,4]`. There is no next greater element, so the answer is `-1`.
+
+### Constraints:
+
+- `1 <= nums1.length <= nums2.length <= 1000`
+- `0 <= nums1[i], nums2[i] <= 10^4`
+- All integers in `nums1` and `nums2` are unique.
+- All the integers of `nums1` also appear in nums2.
+
+## Solution
+
+```py
+class Solution:
+    def nextGreaterElement(self, nums1: list[int], nums2: list[int]) -> list[int]:
+        mono_stack = []
+        next_greater = {}
+
+        for cur in nums2:
+            while mono_stack and cur > mono_stack[-1]:
+                val = mono_stack.pop()
+                next_greater[val] = cur
+            mono_stack.append(cur)
+
+        return [next_greater.get(x, -1) for x in nums1]
+```