题解 | #链表中环的入口结点#

/*
public class ListNode
{
    public int val;
    public ListNode next;
    public ListNode (int x)
    {
        val = x;
    }
}*/
class Solution
{
    public ListNode EntryNodeOfLoop(ListNode pHead)
    {
        // write code here
        if(pHead==null)
            return null;
        ListNode slow=pHead;
        ListNode faster=pHead;
        while(faster!=null && faster.next!=null )
        {
            faster=faster.next.next;
            slow=slow.next;
            if(faster==slow)
                break;
        }
        if(faster==null || faster.next==null)
            return null;
        while(pHead!=faster)
        {
            pHead=pHead.next;
            faster=faster.next;
        }
        return faster;
            
    }
}
如果不借助hash，关键是环的计算