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package LeetCode;

/**

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

* Follow up:

* Can you solve it without using extra space?

* @author Administrator

*

*/

public class HasCycle {

public HasCycle() {

// TODO Auto-generated constructor stub

}

class ListNode {

int val;

ListNode next;

public ListNode(int val) {

this.val = val;

}

}

public boolean hasCycle(ListNode head) {

if (head == null) return false;

ListNode oneStep = head;

ListNode twoStep = head.next;

while (twoStep != null && twoStep.next != null) {

if (oneStep == twoStep) {

return true;

}

oneStep = oneStep.next;

twoStep = twoStep.next.next;

}

return false;

}

}