solve: removeNthNodeFromEndOfList

Author: yolophg

remove-nth-node-from-end-of-list/yolophg.py

@@ -0,0 +1,29 @@
+# Time Complexity: O(N) - go through the list twice (once to count, once to remove).
+# Space Complexity: O(1) - only use a few extra variables.
+
+class Solution:
+    def removeNthFromEnd(self, head: Optional[ListNode], n: int) -> Optional[ListNode]:
+        # count the total number of nodes in the list
+        N = 0
+        curr = head
+        while curr:
+            N += 1
+            curr = curr.next
+        
+        # find the position of the node to remove (from the start)
+        node_to_remove = N - n
+
+        # if need to remove the first node, just return the second node as the new head
+        if node_to_remove == 0:
+            return head.next
+        
+        # traverse again to find the node right before the one we need to remove
+        curr = head
+        for i in range(N - 1):
+            if (i + 1) == node_to_remove:
+                # remove the nth node by skipping it
+                curr.next = curr.next.next
+                break
+            curr = curr.next
+        
+        return head