题解 | #链表中环的入口结点#

/* struct ListNode { int val; struct ListNode next; ListNode(int x) : val(x), next(NULL) { } }; / class Solution { public: ListNode EntryNodeOfLoop(ListNode pHead) { if(!pHead) return nullptr; if(!(pHead -> next)) return nullptr; ListNode* fast = pHead; ListNode* slow = pHead;

    bool flag = 0;
    while(slow -> next && fast -> next && fast -> next -> next)
    {
        slow = slow -> next;
        fast = fast -> next -> next;
        if(slow == fast)
        {
            flag = 1;
            break;
        }
    }
    if(flag)
    {
        auto low = pHead;
        while(low != fast)
        {
            fast = fast -> next;
            low = low -> next;
        }
        return low;
    }
    return nullptr;
}

};