May 6

Author: siddydutta

2024-05-May-LeetCoding-Challenge/README.md

@@ -8,7 +8,7 @@
 | May 3 | [165. Compare Version Numbers](https://leetcode.com/problems/compare-version-numbers/) | Medium | Solved |
 | May 4 | [881. Boats to Save People](https://leetcode.com/problems/boats-to-save-people/) | Medium | Solved |
 | May 5 | [237. Delete Node in a Linked List](https://leetcode.com/problems/delete-node-in-a-linked-list/) | Medium | Solved |
-| May 6 | []() |  |  |
+| May 6 | [2487. Remove Nodes From Linked List](https://leetcode.com/problems/remove-nodes-from-linked-list/) | Medium | Unsolved |
 | May 7 | []() |  |  |
 | May 8 | []() |  |  |
 | May 9 | []() |  |  |
@@ -40,5 +40,5 @@
 | Level  | Problems | Solved | Unsolved |
 | ---    | --- | --- | --- |
 | Easy   | 2 | 2 | 0 |
-| Medium | 3 | 3 | 0 |
+| Medium | 4 | 3 | 1 |
 | Hard   | 0 | 0 | 0 |

2024-05-May-LeetCoding-Challenge/Remove Nodes From Linked List.py

@@ -0,0 +1,59 @@
+from typing import Optional
+
+
+# Definition for singly-linked list.
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+
+class Solution:
+    def removeNodes(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        if head is None or head.next is None:
+            return head
+        # reverse linked list
+        prev, curr = None, head
+        while curr:
+            curr.next, prev, curr = prev, curr, curr.next
+        # filter
+        dummy = ListNode()
+        prev, curr = dummy, prev
+        while curr:
+            if curr.val >= prev.val:
+                prev.next = curr
+                prev = curr
+            curr = curr.next
+        prev.next = None
+        # reverse linked list
+        prev, curr = None, dummy.next
+        while curr:
+            curr.next, prev, curr = prev, curr, curr.next
+        return prev
+
+
+def main():
+    head = ListNode(5)
+    head.next = ListNode(2)
+    head.next.next = ListNode(13)
+    head.next.next.next = ListNode(3)
+    head.next.next.next.next = ListNode(8)
+    head = Solution().removeNodes(head)
+    assert head.val == 13
+    assert head.next.val == 8
+    assert head.next.next is None
+
+    head = ListNode(1)
+    head.next = ListNode(1)
+    head.next.next = ListNode(1)
+    head.next.next.next = ListNode(1)
+    head = Solution().removeNodes(head)
+    assert head.val == 1
+    assert head.next.val == 1
+    assert head.next.next.val == 1
+    assert head.next.next.next.val == 1
+    assert head.next.next.next.next is None
+
+
+if __name__ == '__main__':
+    main()