Completed Linked List-1

Peroblem_3.py

@@ -0,0 +1,20 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+
+class Solution:
+    def detectCycle(self, head):
+        slow, fast = head, head
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next.next
+            if fast == slow:
+                fast = head
+                while fast != slow:
+                    fast = fast.next
+                    slow = slow.next
+                return slow
+        return None

Problem_1.py

@@ -0,0 +1,16 @@
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+class Solution:
+    def reverseList(self, head):
+        self.newHead = None
+        return self.helper(head)
+
+    def helper(self, node):
+        if not node or not node.next:
+            return node
+        curr = self.helper(node.next)
+        node.next.next = node
+        node.next = None
+        return curr

Problem_2.py

@@ -0,0 +1,18 @@
+# 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,n):
+        fast = head
+        for _ in range(n):
+            fast = fast.next
+            if not fast:
+                return head.next
+        slow = head
+        while fast.next:
+            slow = slow.next
+            fast = fast.next
+        slow.next = slow.next.next
+        return head