题目：

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代码(首刷看解析 2024年1月13日）：

class Solution {
public:ListNode *detectCycle(ListNode *head) {if (head == nullptr) return nullptr;ListNode* fast = head;ListNode* slow = head;while (true) {if(fast->next == nullptr || fast->next->next == nullptr) return nullptr;fast = fast->next->next;slow = slow->next;if(fast == slow) break;}fast = head;while (fast != slow) {fast = fast->next;slow = slow->next;}return fast;}
};

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