142. Linked List Cycle2

Linked List Cycle II - LeetCode

Submit Code

def detectCycle(head)
    catchup_node = find_catchup_node(head)
    return nil if catchup_node.nil?

    fast = catchup_node
    slow = head

    while fast != slow
        fast = fast.next
        slow = slow.next
    end

    fast
end

def find_catchup_node(head)
    fast = slow = head

    while fast && fast.next
        fast = fast.next.next
        slow = slow.next

        if fast == slow
            return fast
        end
    end

    nil
end