876. Middle of the Linked List

problem

solution

class Solution {
public:
    ListNode* middleNode(ListNode* head) {
        ListNode *slow = head, *fast = head;
        while(fast && fast->next ){
            fast = fast->next->next;
            slow= slow->next;
        }
        return slow;
        
    }
};

analysis

• time complexity O(n)
• speed complexity O(1)