【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;
}