feat: Linked List 1 complete

LinkedlistcycleII.py

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+'''
+Time: O(N)
+Space: O(1)
+'''
+
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+class Solution:
+    def isCycle(self,slow,fast):
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next.next
+            if slow == fast:
+                return [True, fast]
+        return [False, fast]
+
+    def detectCycle(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        slow = fast = head
+        cycle = self.isCycle(slow,fast)
+        fast = cycle[1]
+        if cycle[0]:
+            while slow != fast:
+                slow = slow.next
+                fast = fast.next
+            return slow 
+        return None
+
+
+
+
+
+
+
+

remove_nth_node_from_end_of_list.py

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+'''
+Time complexity: O(N)
+Space complexity: O(1)
+'''
+# Definition for singly-linked list.
+class ListNode:
+    def __init__(self, x):
+        self.val = x
+        self.next = None
+
+class Solution:
+   class Solution:
+    def removeNthFromEnd(self, head: Optional[ListNode], n: int) -> Optional[ListNode]:
+        dummyNode = ListNode(0,head)
+        slow = dummyNode
+        fast = head 
+
+        while fast and n > 0:
+           fast = fast.next
+           n -= 1
+
+        while fast:
+           slow = slow.next
+           fast = fast.next 
+
+        slow.next = slow.next.next
+
+        return dummyNode.next

reverse_linked_list.py

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+'''
+Iterrative method:
+time complexity: O(N)
+space complexity: O(1)
+
+Recursive method:
+time complexity: O(N)
+space complexity: O(N) 
+'''
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+class Solution:
+    # iterative way
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        if not head or head.next:
+            return head
+        prev = None
+        curr = head 
+        next = None
+
+        while curr:                         
+            next  = curr.next               
+            prev = curr.next 
+            prev = curr
+            curr = next
+        return prev
+
+    #recursive way
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        if not head or not head.next:
+            return head
+
+        new_head = self.reverseList(head.next)
+        head.next.next = head
+        head.next = None
+        return new_head
+
+
+
+
+
+
+