docs: add new problem documentation pages and update redirects

apps/docs/content/(02-nodal-grid)/hybrid-structures/380_insert-delete-getrandom-o1.mdx

@@ -0,0 +1,68 @@
+---
+title: '380. Insert Delete GetRandom O(1)'
+description: 'Implement the RandomizedSet class:'
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "Math", slug: "math" }
+  - { name: "Design", slug: "design" }
+  - { name: "Randomized", slug: "randomized" }
+issue: "https://github.com/prdlk/leetcode/issues/90"
+sidebar:
+  label: 'Insert Delete GetRandom O(1)'
+  badge: 'Medium'
+---
+
+::::warning
+You must implement the functions of the class such that each function works in average O(1) time complexity.
+::::
+
+### Example 1:
+- Input: ``
+- Output: ``
+- Explanation: Input ["RandomizedSet", "insert", "remove", "insert", "getRandom", "remove", "insert", "getRandom"] `[[]`, `[1]`, `[2]`, `[2]`, `[]`, `[1]`, `[2]`, []] Output [null, true, false, true, `2`, true, false, 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts `1` to the set. Returns true as `1` was inserted successfully. randomizedSet.remove(2); // Returns false as `2` does not exist in the set. randomizedSet.insert(2); // Inserts `2` to the set, returns true. Set now contains `[1,2]`. randomizedSet.getRandom(); // getRandom() should return either `1` or `2` randomly. randomizedSet.remove(1); // Removes `1` from the set, returns true. Set now contains `[2]`. randomizedSet.insert(2); // `2` was already in the set, so return false. randomizedSet.getRandom(); // Since `2` is the only number in the set, getRandom() will always return `2`.
+
+### Constraints:
+
+- `-2^31 <= val <= 2^31 - 1`
+- At most 2 * 10^5 calls will be made to insert, remove, and getRandom.
+- There will be at least one element in the data structure when getRandom is called.
+
+## Solution
+
+```py
+from random import choice
+
+
+class RandomizedSet:
+    def __init__(self):
+        self.list = []
+        self.dict = {}
+
+    def insert(self, val: int) -> bool:
+        if val in self.dict:
+            return False
+        self.dict[val] = len(self.list)
+        self.list.append(val)
+        return True
+
+    def remove(self, val: int) -> bool:
+        if val in self.dict:
+            last, idx = self.list[-1], self.dict[val]
+            self.list[idx], self.dict[last] = last, idx
+            self.list.pop()
+            del self.dict[val]
+            return True
+        return False
+
+    def getRandom(self) -> int:
+        return choice(self.list)
+
+
+# Your RandomizedSet object will be instantiated and called as such:
+# obj = RandomizedSet()
+# param_1 = obj.insert(val)
+# param_2 = obj.remove(val)
+# param_3 = obj.getRandom()
+```

apps/docs/content/(02-nodal-grid)/linked-list/19_remove-nth-node-from-end-of-list.mdx

@@ -0,0 +1,64 @@
+---
+title: '19. Remove Nth Node From End of List'
+description: Given the head of a linked list, remove the n^th node from the end of the list and return its head
+icon: dot
+topics:
+  - { name: "Linked List", slug: "linked-list" }
+  - { name: "Two Pointers", slug: "two-pointers" }
+issue: "https://github.com/prdlk/leetcode/issues/80"
+sidebar:
+  label: 'Remove Nth Node From End of List'
+  badge: 'Medium'
+---
+
+::::warning
+Could you do this in one pass?
+::::
+
+### Example 1:
+- Input: `head = [1,2,3,4,5], n = 2`
+- Output: `[1,2,3,5]`
+
+### Example 2:
+- Input: `head = [1], n = 1`
+- Output: `[]`
+
+### Example 3:
+- Input: `head = [1,2], n = 1`
+- Output: `[1]`
+
+### Constraints:
+
+- The number of nodes in the list is sz.
+- `1 <= sz <= 30`
+- `0 <= Node.val <= 100`
+- `1 <= n <= sz`
+
+## Solution
+
+```py
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def removeNthFromEnd(self, head: ListNode | None, n: int) -> ListNode | None:
+        dummy = ListNode(0)
+        dummy.next = head
+
+        fast = dummy
+        for _ in range(n):
+            if fast.next is None:
+                return head
+            fast = fast.next
+
+        slow = dummy
+        while fast.next is not None:
+            slow = slow.next
+            fast = fast.next
+
+        slow.next = slow.next.next
+
+        return dummy.next
+```

apps/docs/content/(02-nodal-grid)/linked-list/82_remove-duplicates-from-sorted-list-ii.mdx

@@ -0,0 +1,53 @@
+---
+title: '82. Remove Duplicates from Sorted List II'
+description: You are given the head of a sorted linked list
+icon: dot
+topics:
+  - { name: "Linked List", slug: "linked-list" }
+  - { name: "Two Pointers", slug: "two-pointers" }
+issue: "https://github.com/prdlk/leetcode/issues/84"
+sidebar:
+  label: 'Remove Duplicates from Sorted List II'
+  badge: 'Medium'
+---
+
+### Example 1:
+- Input: `head = [1,2,3,3,4,4,5]`
+- Output: `[1,2,5]`
+
+### Example 2:
+- Input: `head = [1,1,1,2,3]`
+- Output: `[2,3]`
+
+### Constraints:
+
+- The number of nodes in the list is in the range [0, 300].
+- `-100 <= Node.val <= 100`
+- The list is guaranteed to be sorted in ascending order.
+
+## Solution
+
+```py
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def deleteDuplicates(self, head: ListNode | None) -> ListNode | None:
+        sentinel = ListNode(0, head)
+        pred = sentinel
+
+        while head:
+            if head.next and head.val == head.next.val:
+                while head.next and head.val == head.next.val:
+                    head = head.next
+
+                pred.next = head.next
+            else:
+                pred = pred.next
+
+            head = head.next
+
+        return sentinel.next
+```

apps/docs/content/(02-nodal-grid)/linked-list/876_middle-of-the-linked-list.mdx

@@ -0,0 +1,45 @@
+---
+title: '876. Middle of the Linked List'
+description: Given the head of a singly linked list, return the middle node of the linked list
+icon: dot
+topics:
+  - { name: "Linked List", slug: "linked-list" }
+  - { name: "Two Pointers", slug: "two-pointers" }
+issue: "https://github.com/prdlk/leetcode/issues/82"
+sidebar:
+  label: 'Middle of the Linked List'
+  badge: 'Easy'
+---
+
+### Example 1:
+- Input: `head = [1,2,3,4,5]`
+- Output: `[3,4,5]`
+- Explanation: The middle node of the list is node `3`.
+
+### Example 2:
+- Input: `head = [1,2,3,4,5,6]`
+- Output: `[4,5,6]`
+- Explanation: Since the list has two middle nodes with values `3` and `4`, we return the second one.
+
+### Constraints:
+
+- The number of nodes in the list is in the range [1, 100].
+- `1 <= Node.val <= 100`
+
+## Solution
+
+```py
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def middleNode(self, head: ListNode | None) -> ListNode | None:
+        slow = fast = head
+        while fast and fast.next:
+            fast = fast.next.next
+            slow = slow.next
+
+        return slow
+```

apps/docs/content/(02-nodal-grid)/linked-list/92_reverse-linked-list-ii.mdx

@@ -0,0 +1,65 @@
+---
+title: '92. Reverse Linked List II'
+description: Given the head of a singly linked list and two integers left and right where left <= right, reverse the nodes of the list from position left to position right, and return the reversed list
+icon: dot
+topics:
+  - { name: "Linked List", slug: "linked-list" }
+issue: "https://github.com/prdlk/leetcode/issues/83"
+sidebar:
+  label: 'Reverse Linked List II'
+  badge: 'Medium'
+---
+
+::::warning
+Could you do it in one pass?
+::::
+
+### Example 1:
+- Input: `head = [1,2,3,4,5], left = 2, right = 4`
+- Output: `[1,4,3,2,5]`
+
+### Example 2:
+- Input: `head = [5], left = 1, right = 1`
+- Output: `[5]`
+
+### Constraints:
+
+- The number of nodes in the list is n.
+- `1 <= n <= 500`
+- `-500 <= Node.val <= 500`
+- `1 <= left <= right <= n`
+
+## Solution
+
+```py
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def reverseBetween(
+        self, head: ListNode | None, left: int, right: int
+    ) -> ListNode | None:
+        cur, prev = head, None
+        while left > 1:
+            prev = cur
+            cur = cur.next
+            left, right = left - 1, right - 1
+
+        tail, con = cur, prev
+        while right:
+            third = cur.next
+            cur.next = prev
+            prev = cur
+            cur = third
+            right -= 1
+
+        if con:
+            con.next = prev
+        else:
+            head = prev
+
+        tail.next = cur
+        return head
+```

apps/docs/content/(02-nodal-grid)/matrix-index-math/36_valid-sudoku.mdx

@@ -0,0 +1,57 @@
+---
+title: '36. Valid Sudoku'
+description: 'Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:'
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "Matrix", slug: "matrix" }
+issue: "https://github.com/prdlk/leetcode/issues/94"
+sidebar:
+  label: 'Valid Sudoku'
+  badge: 'Medium'
+---
+
+### Example 1:
+- Input: `board = [["5","3",".",".","7",".",".",".","."] ,["6",".",".","1","9","5",".",".","."] ,[".","9","8",".",".",".",".","6","."] ,["8",".",".",".","6",".",".",".","3"] ,["4",".",".","8",".","3",".",".","1"] ,["7",".",".",".","2",".",".",".","6"] ,[".","6",".",".",".",".","2","8","."] ,[".",".",".","4","1","9",".",".","5"] ,[".",".",".",".","8",".",".","7","9"]]`
+- Output: `true`
+
+### Example 2:
+- Input: `board = [["8","3",".",".","7",".",".",".","."] ,["6",".",".","1","9","5",".",".","."] ,[".","9","8",".",".",".",".","6","."] ,["8",".",".",".","6",".",".",".","3"] ,["4",".",".","8",".","3",".",".","1"] ,["7",".",".",".","2",".",".",".","6"] ,[".","6",".",".",".",".","2","8","."] ,[".",".",".","4","1","9",".",".","5"] ,[".",".",".",".","8",".",".","7","9"]]`
+- Output: `false`
+- Explanation: Same as Example `1`, except with the `5` in the top left corner being modified to `8`. Since there are two 8's in the top left 3x3 sub-box, it is invalid.
+
+### Constraints:
+
+- `board.length == 9`
+- `board[i].length == 9`
+- board[i][j] is a digit 1-9 or '.'.
+
+## Solution
+
+```py
+import collections
+
+
+class Solution:
+    def isValidSudoku(self, board: list[list[str]]) -> bool:
+        cols = collections.defaultdict(set)
+        rows = collections.defaultdict(set)
+        squares = collections.defaultdict(set)  # (r/3, c/3)
+
+        for r in range(9):
+            for c in range(9):
+                if board[r][c] == ".":
+                    continue
+                if (
+                    board[r][c] in rows[r]
+                    or board[r][c] in cols[c]
+                    or board[r][c] in squares[(r // 3, c // 3)]
+                ):
+                    return False
+                cols[c].add(board[r][c])
+                rows[r].add(board[r][c])
+                squares[(r // 3, c // 3)].add(board[r][c])
+
+        return True
+```

apps/docs/redirects.ts

@@ -7,12 +7,14 @@ export default [
   { from: "/4", to: "/binary-search/median-of-two-sorted-arrays" },
   { from: "/11", to: "/two-pointers/container-with-most-water" },
   { from: "/15", to: "/two-pointers/3sum" },
+  { from: "/19", to: "/linked-list/remove-nth-node-from-end-of-list" },
   { from: "/20", to: "/stack/valid-parentheses" },
   { from: "/21", to: "/linked-list/merge-two-sorted-lists" },
   { from: "/23", to: "/heap-priority-queue/merge-k-sorted-lists" },
   { from: "/33", to: "/binary-search/search-in-rotated-sorted-array" },
   { from: "/34", to: "/binary-search/find-first-and-last-position-of-element-in-sorted-array" },
   { from: "/35", to: "/binary-search/search-insert-position" },
+  { from: "/36", to: "/matrix-index-math/valid-sudoku" },
   { from: "/39", to: "/backtracking/combination-sum" },
   { from: "/42", to: "/two-pointers/trapping-rain-water" },
   { from: "/46", to: "/backtracking/permutations" },
@@ -32,7 +34,9 @@ export default [
   { from: "/76", to: "/sliding-window/minimum-window-substring" },
   { from: "/78", to: "/backtracking/subsets" },
   { from: "/80", to: "/two-pointers/remove-duplicates-from-sorted-array-ii" },
+  { from: "/82", to: "/linked-list/remove-duplicates-from-sorted-list-ii" },
   { from: "/84", to: "/monotonic-stack/largest-rectangle-in-histogram" },
+  { from: "/92", to: "/linked-list/reverse-linked-list-ii" },
   { from: "/98", to: "/binary-search-tree/validate-binary-search-tree" },
   { from: "/102", to: "/tree-bfs/binary-tree-level-order-traversal" },
   { from: "/104", to: "/tree-dfs/maximum-depth-of-binary-tree" },
@@ -75,6 +79,7 @@ export default [
   { from: "/323", to: "/union-find/number-of-connected-components-in-an-undirected-graph" },
   { from: "/344", to: "/two-pointers/reverse-string" },
   { from: "/347", to: "/hash-table/top-k-frequent-elements" },
+  { from: "/380", to: "/hybrid-structures/insert-delete-getrandom-o1" },
   { from: "/387", to: "/hash-table/first-unique-character-in-a-string" },
   { from: "/392", to: "/two-pointers/is-subsequence" },
   { from: "/417", to: "/graph-dfs/pacific-atlantic-water-flow" },
@@ -91,6 +96,7 @@ export default [
   { from: "/739", to: "/monotonic-stack/daily-temperatures" },
   { from: "/853", to: "/monotonic-stack/car-fleet" },
   { from: "/875", to: "/binary-search/koko-eating-bananas" },
+  { from: "/876", to: "/linked-list/middle-of-the-linked-list" },
   { from: "/901", to: "/monotonic-stack/online-stock-span" },
   { from: "/973", to: "/heap-priority-queue/k-closest-points-to-origin" },
   { from: "/974", to: "/prefix-sum/subarray-sums-divisible-by-k" },