题目描述. - 力扣（LeetCode）：

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答案展示:

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* middleNode(struct ListNode* head) {
 
    struct ListNode* fast,*slow;
    fast = slow = head;
    while(fast&&fast->next)
    {
        fast = fast->next->next;
        slow = slow->next;
    }

    return slow;
}

亮点：双指针