【leetcode】【单链表】【25】Reverse Nodes in k-Group

#include<iostream>
#include<stack>
#include<memory>
using namespace std;

struct ListNode {
int val;
ListNode *next;
ListNode(int x) : val(x), next(NULL) {}
};

class Solution {
public:
pair<ListNode*,ListNode*> reverseList(ListNode* head) {
if (head == NULL || head->next == NULL)
return pair<ListNode*, ListNode*>(head, head);

ListNode* cur = head;
ListNode* newHead = NULL;
ListNode* temp = NULL;
while (cur){
temp = cur;
cur = cur->next;
temp->next = newHead;
newHead = temp;
}
return pair<ListNode*, ListNode*>(newHead, head); //返回反转后的头结点和尾结点（尾节点不是NULL，是NULL前面一个节点）
}
ListNode* reverseKGroup(ListNode* head, int k) {
if (head == NULL || head->next == NULL)
return head;

int numOfNodes = 0; //链表长度
ListNode* cur = head;
while (cur){
++numOfNodes;
cur = cur->next;
}
if (numOfNodes < k || k==1) //长度小于k或者k==1直接返回
return head;

int kgroup = numOfNodes / k; //分为几组

ListNode* temp = new ListNode(0);
ListNode* beforeHead = temp;

ListNode* newHead = NULL;
ListNode* newTail = NULL;
while (kgroup>0){
newHead = cur = head;
for (int i = 1; i < k; ++i)
cur = cur->next;
head = cur->next;
cur->next = NULL;

pair<ListNode*, ListNode*> pr = reverseList(newHead);
newHead = pr.first;
newTail = pr.second;

////for test
//ListNode* aa = newHead;
//while (aa){
//	cout << aa->val << " ";
//	aa = aa->next;
//}
//cout << endl;
temp->next = newHead;
temp = newTail;
--kgroup;
}
if (head)
temp->next = head;
head = beforeHead->next;
delete beforeHead;
return head;
}
ListNode* createList(ListNode* head){
int numOfNode;
int value;
cout << "please input number of listNode:";
cin >> numOfNode;
cin >> value;
head = new ListNode(value);
ListNode* cur = head;
for (int i = 1; i < numOfNode; ++i){
cin >> value;
ListNode* temp = new ListNode(value);
cur->next = temp;
cur = temp;
}
return head;
}
void printNode(ListNode* head){
ListNode* cur = head;
while (cur){
cout << cur->val << " ";
cur = cur->next;
}
cout << endl;
}
};

int main(){
ListNode* head = NULL;
Solution solution;
head = solution.createList(head);
solution.printNode(head);

head = solution.reverseKGroup(head,3);
solution.printNode(head);

system("pause");
return 0;
}