题解 | #链表中的节点每k个一组翻转#

```/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 * };
 *
 * C语言声明定义全局变量请加上static，防止重复定义
 */

/**
 * 
 * @param lists ListNode类一维数组 
 * @param listsLen int lists数组长度
 * @return ListNode类
 * Divide and Conquer
 * 0 1 2 3 4 5 6 7 8;
 * (0,1) (2,3) (4,5) (6,7) 8; divide;
 * (0,1)->10 (2,3)->23 (4,5)->45 (6,7)->67 8->8;conquer;critical:0 1 return 10;
 * 10 23 45 67 8 divide
 * (10,23) (45,67) 8
 * (10,23)->1023 (45,67)->4567 8->8;conquer;
 * 1023 4567 8;
 * (1023,4567) 8 ;divide;
 * (1023,4567)->10234567 8->8 conquer
 * (10234567,8) divide;
 * (10234567,8)->102345678;
 * finished;
 */
struct ListNode* merge2(struct ListNode* p, struct ListNode *q ) { // Conquer
    struct ListNode *head, *tool, *headtrave, *Trav1, *Trav2;
    Trav1 = p;
    head = NULL;
    headtrave = head;
    Trav2 = q;
    if(Trav1 == NULL && Trav2 == NULL) return NULL;
    if(Trav1 != NULL && Trav2 == NULL) return Trav1;
    if(Trav1 == NULL && Trav2 != NULL) return Trav2;
    while(Trav1 && Trav2) {
        if(Trav1->val >= Trav2->val) {
            if(headtrave == NULL) {
                headtrave = Trav2;
                head = Trav2;
                Trav2 = Trav2->next;
                head->next = NULL;
            } else {
                tool = Trav2;
                Trav2 = Trav2->next;
                tool->next = headtrave->next;
                headtrave->next = tool;
                headtrave = tool;
            }
        } else {
            if(headtrave == NULL) {
                headtrave = Trav1;
                head = Trav1;
                Trav1 = Trav1->next;
                head->next = NULL;
            } else {
                tool = Trav1;
                Trav1 = Trav1->next;
                tool->next = headtrave->next;
                headtrave->next = tool;
                headtrave = tool;
            }
        }
    }
    headtrave->next = Trav1?Trav1:Trav2;
    return head;
}
struct ListNode* merge(struct ListNode** lists, int Left, int Right) { // Divide;
    if(Left > Right) {
        return NULL;
    } 
    if(Left == Right) {
        return lists[Left];
    }
    int Mid = (Left+Right)/2;
    return merge2(merge(lists, Left, Mid), merge(lists, Mid+1, Right));
}
struct ListNode* mergeKLists(struct ListNode** lists, int listsLen ) {
    // write code here
    if(listsLen == 0) {return NULL;}
    if(listsLen == 1) {return lists[0];}
    return merge(lists,0,listsLen-1);

    
}