Reverse_Nodes_In_K-Group.cpp

struct ListNode {
	int val;
	ListNode *next;
	ListNode(int x) : val(x), next(NULL) {}
};
 
class Solution {
public:
    /**
     * @param head a ListNode
     * @param k an integer
     * @return a ListNode
     */
     ListNode *reverse(ListNode *p1, ListNode *p2){
     	ListNode *p1next = p1->next;
     	ListNode *p2next = p2->next;
     	ListNode *prev = p2next;
     	ListNode *p = p1next;

     	while(p != p2next){
     		ListNode *temp = p->next;
     		p->next = prev;
     		prev = p;
     		p = temp;
     	}
     	p1->next = p2;
     	return p1next;
     }

     ListNode *reverseKGroup(ListNode *head, int k){
     	if(k == 1) return head;
     	ListNode *dummy = new ListNode(0);
     	dummy->next = head;

     	ListNode *p1 = dummy, *p2 = dummy;
     	for(int i = 0; i < k; i++){
     		if(p2 == NULL){
     			break;
     		}
     		p2 = p2->next;
     	}

     	if(p2 == NULL) return head;

     	while(p2 != NULL){
     		p2 = reverse(p1, p2);
     		for(int i = 0; i < k; i++){
     			if(p2 == NULL){
     				break;
     			}
     			p1 = p1->next;
     			p2 = p2->next;
     		}
     	}
     	return dummy->next;
     }
};

int main(){
	// do sth 
	return 0;
}