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LinkedListCycleII.java
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24 lines (24 loc) · 777 Bytes
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public class LinkedListCycleII {
/**
* 这里有个问题，如果链表是a,b，然后又回到a
* 则slow和fast必须都从head起步才行
* 如果slow从head起步，fast从head.next起步，则这里会死循环
*/
public ListNode detectCycle(ListNode head) {
ListNode slow = head, fast = head;
boolean hasCycle = false;
for (; fast != null && fast.next != null; ) {
slow = slow.next;
fast = fast.next.next;
if (slow == fast) {
hasCycle = true;
break;
}
}
if (!hasCycle) {
return null;
}
for (ListNode node = head; node != slow; node = node.next, slow = slow.next);
return slow;
}
}