代码实现：

/*** Definition for singly-linked list.* struct ListNode {*     int val;*     struct ListNode *next;* };*/
struct ListNode* merge(struct ListNode *l1, struct ListNode *l2) {if (l1 == NULL) {return l2;}if (l2 == NULL) {return l1;}struct ListNode *head = malloc(sizeof(*head)); // 设置虚拟头结点struct ListNode *tail = head;while (l1 && l2) {if (l1->val < l2->val) {tail->next = l1;l1 = l1->next;} else {tail->next = l2;l2 = l2->next;}tail = tail->next;tail->next = NULL;}if (l1) {tail->next = l1;}if (l2) {tail->next = l2;}struct ListNode *result = head->next;head->next = NULL;free(head);return result;   
}struct ListNode* mergeKLists(struct ListNode **lists, int listsSize){if (lists == NULL || listsSize == 0) {return NULL;}struct ListNode *h = NULL;for (int i = 0; i < listsSize; i++) {h = merge(lists[i], h);}return h;
}