141. Linked List Cycle
Description
Given 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 next
pointer. Internally, pos
is used to denote the index of the node that tail's next
pointer is connected to. Note that pos
is not passed as a parameter.
Return true
if there is a cycle in the linked list. Otherwise, return false
.
Constraints
The number of the nodes in the list is in the range
[0, 104]
.-105 <= Node.val <= 105
pos
is-1
or a valid index in the linked-list.
Approach
Links
GeeksforGeeks
ProgramCreek
YouTube
Examples
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).
Solutions
// Definition for singly-linked list.
class ListNode {
int val;
ListNode next;
ListNode(int x) {
val = x;
next = null;
}
}
Follow up
Can you solve it using
O(1)
(i.e. constant) memory?
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