Consider we have a linked list, and we have to check whether there is any cycle or not. To represent the cycle in the given linked list, we will use one integer pointer called pos. This pos represents a position in the linked list where tail is connected. So if pos is -1, then there is no cycle present in the linked list. For example, the linked list is like [5, 3, 2, 0, -4, 7], and pos = 1. So there is a cycle, and tail is connected to the second node.
To solve this, we will follow these steps −
Let us see the following implementation to get better understanding −
class ListNode: def __init__(self, data, next = None): self.data = data self.next = next def make_list(elements): head = ListNode(elements) for element in elements[1:]: ptr = head while ptr.next: ptr = ptr.next ptr.next = ListNode(element) return head def get_node(head, pos): if pos != -1: p = 0 ptr = head while p < pos: ptr = ptr.next p += 1 return ptr class Solution(object): def hasCycle(self, head): hashS = set() while head: if head in hashS: return True hashS.add(head) head = head.next return False head = make_list([5,3,2,0,-4,7]) last_node = get_node(head, 5) pos = 1 last_node.next = get_node(head, pos) ob1 = Solution() print(ob1.hasCycle(head))
List = [5,3,2,0,-4,7] Pos = 1