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LinkedListCycle.java
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LinkedListCycle.java
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/**
* Given a linked list, determine if it has a cycle in it.
* <p>
* Follow up:
* Can you solve it without using extra space?
*/
public class LinkedListCycle {
// Time limit exceeded.
/*public boolean hasCycle(ListNode head) {
if (head == null || head.next == null) {
return false;
}
ListNode node = head.next;
while (node != head) {
if (node == null) {
return false;
}
node = node.next;
}
return true;
}*/
// Accepted.
public boolean hasCycle(ListNode head) {
ListNode slow = head, fast = head;
while (fast != null && fast.next != null) {
slow = slow.next;
fast = fast.next.next;
if (slow == fast) {
return true;
}
}
return false;
}
public static class ListNode {
int val;
ListNode next;
ListNode(int x) {
val = x;
next = null;
}
}
}