JZ55 链表中环的入口结点

https://www.nowcoder.com/practice/253d2c59ec3e4bc68da16833f79a38e4

这题用左神的做法，快慢指针，两指针相遇时，快指针回到起点（步数变为与慢指针一致），再次相遇就是起点

public class Solution {
    public ListNode EntryNodeOfLoop(ListNode pHead) {
        if (pHead == null || pHead.next == null) return null;
        ListNode slow = pHead;
        ListNode fast = pHead;
        
        do {
            if (fast == null || fast.next == null) return null;
            slow = slow.next;
            fast = fast.next.next;
        } while (slow != fast);
        
        fast = pHead;
        
        while (slow != fast) {
            slow = slow.next;
            fast = fast.next;
        }
        
        return fast;
    }
}

就不去证明了