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->next == NULL) return NULL;
    struct ListNode* run = pHead;
    struct ListNode* man = pHead;
    while(run && man){
        run=run->next->next;
        man=man->next;
        if(run==man){
            break;
        }
    }
    if(run == NULL || man==NULL) return NULL;
    if(run == pHead) return pHead;
    man = pHead;
    while(true){
        man = man->next;
        run = run->next;
        if(man == run){
            return man;
        }
    }

}