JZ55 链表中环的入口结点

本文最后更新于：2022年4月9日 中午

image-20211010152739699

Solution

  • 快慢指针
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/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
        val(x), next(NULL) {
    }
};
*/
class Solution {
public:
    ListNode* EntryNodeOfLoop(ListNode* pHead)
    {
        ListNode *fast = pHead;
        ListNode *slow = pHead;
        while (fast && fast->next) {
            fast = fast->next->next;
            slow = slow->next;
            if (fast == slow) break;
        }
        if (!fast || !fast->next) return nullptr;
        fast = pHead;
        while (fast != slow) {
            fast = fast->next;
            slow = slow->next;
        }
        return fast;
    }
};