head, the head of a linked list, determine if the linked list has a cycle in it.
There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the
posis used to denote the index of the node that tail’s
nextpointer is connected to. Note that
posis not passed as a parameter.
trueif there is a cycle in the linked list. Otherwise, return
flowchart LR a((3))-->b((2)) b-->c((0)) c-->d(("-4")) d-->b
Input: head = [3,2,0,-4], pos = 1 Output: true Explanation: There is a cycle in the linked list, where the tail connects to the 1st node (0-indexed).
flowchart LR a((1))-->b((2)) b-->a
Input: head = [1,2], pos = 0 Output: true Explanation: There is a cycle in the linked list, where the tail connects to the 0th node.
flowchart LR a((1))
Input: head = , pos = -1 Output: false Explanation: There is no cycle in the linked list.
# 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: """ T: O(N) S: O(N) """ mp = set() curr = head while curr and curr.next: if curr in mp: return True else: mp.add(curr) curr = curr.next return False