feat: add middle-of-the-linked-list

scarowar · scarowar · commit 2fda23a20bd4 · 2025-06-14T13:03:04.000+05:30
diff --git a/problems/0021-merge-two-sorted-lists/solution.py b/problems/0021-merge-two-sorted-lists/solution.py
@@ -13,7 +13,7 @@ def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) ->
         p1 = list1
         p2 = list2
 
-        while p1 is not None and p2 is not None:
+        while p1 and p2:
             if p1.val < p2.val:
                 p.next = p1
                 p1 = p1.next
@@ -22,10 +22,10 @@ def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) ->
                 p2 = p2.next
             p = p.next
             
-        if p1 is not None:
+        if p1:
             p.next = p1
 
-        if p2 is not None:
+        if p2:
             p.next = p2
         
         return dummy.next
diff --git a/problems/0876-middle-of-the-linked-list/README.md b/problems/0876-middle-of-the-linked-list/README.md
@@ -0,0 +1,18 @@
+# Problem 0876: Middle Of The Linked List
+
+## Link
+https://leetcode.com/problems/middle-of-the-linked-list/
+
+## Intuition
+Use two pointers moving at different speeds to find the middle efficiently in a single pass.
+
+## Approach
+Initialize fast and slow pointers at the head; move fast by two steps and slow by one until fast reaches the end, then return slow.
+
+## Complexity
+- Time complexity: O(n), as each node is visited at most once.
+- Space complexity: O(1), using only two pointers regardless of list size.
+
+## Notes
+Alternate: count nodes then index to middle; for even length, returns second middle; handles empty/one-node lists gracefully.
+
diff --git a/problems/0876-middle-of-the-linked-list/solution.py b/problems/0876-middle-of-the-linked-list/solution.py
@@ -0,0 +1,40 @@
+from typing import *
+
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+class Solution:
+    def middleNode(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        fast, slow = head, head
+
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next.next
+        
+        return slow
+
+if __name__ == "__main__":
+    def build_list(arr):
+        dummy = ListNode()
+        curr = dummy
+        for v in arr:
+            curr.next = ListNode(v)
+            curr = curr.next
+        return dummy.next
+
+    def to_list(node):
+        res = []
+        while node:
+            res.append(node.val)
+            node = node.next
+        return res
+
+    s = Solution()
+    list1 = build_list([1,2,3,4,5])
+    list2 = build_list([1,2,3,4,5,6])
+    answer_one = s.middleNode(list1)
+    answer_two = s.middleNode(list2)
+    print(to_list(answer_one))  # Expected: [3,4,5]
+    print(to_list(answer_two))  # Expected: [4,5,6]
diff --git a/problems/README.md b/problems/README.md
@@ -6,3 +6,4 @@
 | 0021 | Merge Two Sorted Lists | [0021-merge-two-sorted-lists](0021-merge-two-sorted-lists) |
 | 0217 | Contains Duplicate | [0217-contains-duplicate](0217-contains-duplicate) |
 | 0707 | Design Linked List | [0707-design-linked-list](0707-design-linked-list) |
+| 0876 | Middle Of The Linked List | [0876-middle-of-the-linked-list](0876-middle-of-the-linked-list) |
