Middle of the Linked List

Given a non-empty, singly linked list with head nodehead, 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.

Solution

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode middleNode(ListNode head) {
        ListNode slow = head;
        ListNode fast = head;
        while (fast != null && fast.next != null) {
            slow = slow.next;
            fast = fast.next.next;
        }
        return slow;
    }
}

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