题解 | #链表中环的入口结点#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 * };
 */
/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 * 
 * @param pHead ListNode类 
 * @return ListNode类
 */
struct ListNode* EntryNodeOfLoop(struct ListNode* pHead ) {
    // write code here
    if(pHead == NULL || pHead->next == NULL)
        return NULL;
    struct ListNode *slow = pHead->next;
    struct ListNode *fast = pHead->next->next;

    while(fast != NULL && fast->next != NULL)
    {
        if(fast == slow)
        {
            slow = pHead;
            while(slow != fast)
            {
                slow = slow->next;
                fast = fast->next;
            }
            return slow;
        }
        slow = slow->next;
        fast = fast->next->next;
    }
    return NULL;

}