邏輯比較簡單， 但是感覺對連結串列的掌握程度不夠，需要重新學習一遍連結串列的基本操作。

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        ListNode* HeadNode = new ListNode(0);
        ListNode* MergeNode = HeadNode;
        while((l1 != NULL)&&(l2 != NULL))
        {
            if(l1->val >= l2->val)
            {
                MergeNode->next = l2;
                l2 = l2->next;
            }
            else
            {
                MergeNode->next = l1;
                l1 = l1->next;
            }
            MergeNode = MergeNode->next;
        }
        while(l1 != NULL)
        {
            MergeNode->next = l1;
            l1 = l1->next;
            MergeNode = MergeNode->next;
        }
        while(l2 != NULL)
        {
            MergeNode->next = l2;
            l2 = l2->next;
            MergeNode = MergeNode->next;
        }
        return HeadNode->next;
    }
};