[LeetCode] Problem 876 - Middle of the Linked List

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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

No.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.

No.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.

Code

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public class ListNode {
    int val;
    ListNode next;
    ListNode(int x) { val = x; }
}
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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;
}