Python_100DaysofCode/Linked_List_Cycle_Day43.py at main · ayushlingayat/Python_100DaysofCode · GitHub

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#Brute Approach

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def hasCycle(self, head: Optional[ListNode]) -> bool:
        visited = set()
        current = head

        while current:
            if current in visited:
                return True
            visited.add(current)
            current = current.next

        return False

# TC - O(N)
# SC - O(N)

#Optimal Approach

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def hasCycle(self, head: Optional[ListNode]) -> bool:
        slow = head
        fast = head

        while fast and fast.next:
            slow = slow.next
            fast = fast.next.next

            if slow == fast:
                return True

        return False


# TC - O(n)
# SC - O(1)