下面图片中的这个内容要怎么做，该如何去解决它呢

下面图片中的这个内容要怎么做，我不会做，我该如何去解决它呢？

/**
 * struct ListNode {
 *    int val;
 *    struct ListNode *next;
 * };
 */

class Solution {
public:
    ListNode* get_middle_position(ListNode* head,ListNode* tail)
    {
        ListNode* slow,*fast;
        slow = head;
        fast = head;
        while(fast != tail && fast->next != tail)
        {
            slow = slow->next;
            fast = fast->next->next;
        }
        return slow;
    }
    ListNode* merge(ListNode* left,ListNode* right)
    {
        ListNode *head, *cur;
        if (left->val < right->val)
        {
            head = left;
            left = left->next;
        }
        else
        {
            head = right;
            right = right->next;
        }
        cur = head;
        while (left && right)
        {
            if (left->val < right->val)
            {
                cur->next = left;
                left = left->next;
                cur = cur->next;
            }
            else
            {
                cur->next = right;
                right = right->next;
                cur = cur->next;
            }
        }
        if (left)
        {
            cur->next = left;
        }
        if (right)
        {
            cur->next = right;
        }
        return head;
    }
    ListNode* MergeSort(ListNode* begin, ListNode* mid, ListNode* end)
    {
        if (begin->next == end)
        {
            begin->next = nullptr;
            return begin;
        }
        return merge(MergeSort(begin, get_middle_position(begin, mid), mid), MergeSort(mid, get_middle_position(mid, end), end));
    }
    /**
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    ListNode* sortList(ListNode* head) {
        // write code here
        if(head == NULL)
            return NULL;
        return MergeSort(head,get_middle_position(head, NULL),NULL);
    }
};