middle-of-the-linked-list.java

// Given the head of a singly linked list, return the middle node of the linked list.
//
// If there are two middle nodes, return the second middle node.
//
//  
// Example 1:
//
//
// Input: head = [1,2,3,4,5]
// Output: [3,4,5]
// Explanation: The middle node of the list is node 3.
//
//
// Example 2:
//
//
// Input: head = [1,2,3,4,5,6]
// Output: [4,5,6]
// Explanation: Since the list has two middle nodes with values 3 and 4, we return the second one.
//
//
//  
// Constraints:
//
//
// 	The number of nodes in the list is in the range [1, 100].
// 	1 <= Node.val <= 100
//
//


/**
 * 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, fast = head;
        while (fast != null && fast.next != null) {
            slow = slow.next;
            fast = fast.next.next;
        }
        return slow;
    }
}