Loop Solution - Linked List Cycle

The noticeable part is to verify both twoStepLoop is not null and twoStepLoop.next is not null either… as it jumps two steps and has a command like twoStepLoop.next.next.


/**
 * 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 || head.next == null){
            return false;
        }
        ListNode oneStep = head;
        ListNode twoStep = head.next.next;
        while(twoStep != null && twoStep.next != null){
            if(oneStep == twoStep){
                return true;
            }
            oneStep = oneStep.next;
            twoStep = twoStep.next.next;
        }
        return false;
    }
}