HàPhan 河

Day 8 of 30 days Leetcode challenge

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.


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


It's just a simple Linked List problem. Use fast and slow technique to solve

class Solution {
    func middleNode(_ head: ListNode?) -> ListNode? {
        var slowNode = head
        var fastNode = head?.next
        while(fastNode != nil) {
            slowNode = slowNode?.next
            fastNode = fastNode?.next?.next
        return slowNode