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.

# @lc code=start
using LeetCode

# double pointers
function middle_node_by_double_pointers(head::ListNode)::ListNode
    p1 = p2 = head
    while !isnothing(p2)
        p2 = next(p2)
        isnothing(p2) && return p1
        p2, p1 = p2.next, p1.next
    end
    return p1
end

# @lc code=end

middle_node_by_double_pointers (generic function with 1 method)

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