关于有环链表的若干问题总结

public boolean hasCircle(ListNode pHead) {
if(pHead == null)
return false;

ListNode fast = pHead, slow = pHead;

while(fast != null) {
if(fast.next != null)
fast = fast.next.next;
else
fast = fast.next;

slow = slow.next;

if(fast == slow)
return true;
}

if(fast == null)
return false;
}

public int lenOfCircle(ListNode pHead) {
if(pHead == null)
return 0;

ListNode fast = pHead, slow = pHead;

while(fast != null) {
if(fast.next != null)
fast = fast.next.next;
else
fast = fast.next;

slow = slow.next;

if(fast == slow)
break;
}

if(fast == null)
return 0;

int len = 1;
slow = slow.next;
while(slow != fast) {
slow = slow.next;
len++;
}

return len;
}/*
public class ListNode {
int val;
ListNode next = null;

ListNode(int val) {
this.val = val;
}
}
*/
public class Solution {

public ListNode EntryNodeOfLoop(ListNode pHead)
{
if(pHead == null)
return null;

ListNode pNode, fast = pHead, slow = pHead;

while(fast != null && fast.next != null) {
fast = fast.next.next;
slow = slow.next;

if(fast == slow)
break;
}

if(fast == null || fast.next == null)
return null;

slow = pHead;
while(slow != fast) {
fast = fast.next.next;
slow = slow.next;
}

return slow;
}
}