876. Middle of the Linked List

876. Middle of the Linked List

Given a non-empty, singly linked list with head node head, return a middle node of linked list.

If there are two middle nodes, return the second middle node.

 

Example 1:

Input: [1,2,3,4,5]
Output: Node 3 from this list (Serialization: [3,4,5])
The returned node has value 3.  (The judge's serialization of this node is [3,4,5]).
Note that we returned a ListNode object ans, such that:
ans.val = 3, ans.next.val = 4, ans.next.next.val = 5, and ans.next.next.next = NULL.

Example 2:

Input: [1,2,3,4,5,6]
Output: Node 4 from this list (Serialization: [4,5,6])
Since the list has two middle nodes with values 3 and 4, we return the second one.

 

Note:

• The number of nodes in the given list will be between 1 and 100.'

class Solution {
    public ListNode middleNode(ListNode head) {
        if(head == null) return null;
        ListNode slow = head, fast = head, cur = head;
        int l = 0;
        while(cur != null){l++; cur = cur.next;}
        while(fast != null && fast.next != null && fast.next.next != null){
            slow = slow.next;
            fast = fast.next.next;
        }
        return l % 2 == 0 ? slow.next : slow;
    }
}

这活不行，再整个

class Solution {
    public ListNode middleNode(ListNode head) {
        if(head == null) return null;
        ListNode slow = head, fast = head;
        while(fast != null && fast.next != null){
            slow = slow.next;
            fast = fast.next.next;
        }
        return slow;
    }
}