linkedListCycle.java

/*

Given a linked list, determine if it has a cycle in it.

To represent a cycle in the given linked list, we use an integer pos which represents the position (0-indexed) in the linked list where tail connects to. If pos is -1, then there is no cycle in the linked list.

https://leetcode.com/problems/linked-list-cycle/
*/

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
	public boolean hasCycle(ListNode head) {
		if(head == null) return false;
		ListNode slow = head;
		ListNode fast = head;
		while(fast.next!=null && fast.next.next!=null) {
			slow = slow.next;
			fast = fast.next.next;
			if(slow == fast) return true;
		}
		return false;
	}
}