【leetcode】【单链表】【143】Reorder List

#include<iostream>
using namespace std;

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

class Solution {
public:
	//翻转链表
	ListNode* reverseList(ListNode* head) {
		ListNode* cur = head;
		ListNode* new_head = NULL;
		while (cur){
			ListNode* temp = cur;
			cur = cur->next;
			temp->next = new_head;
			new_head = temp;
		}
		head = new_head;
		return head;
	}
	void reorderList(ListNode* head) {
		if (head == NULL || head->next == NULL)
			return;
		ListNode* slow = head;
		ListNode* fast = head;
		ListNode* last = head;
		//得到list的中点
		while (fast&&fast->next){
			last = slow;
			slow = slow->next;
			fast = fast->next->next;
		}
		last->next = NULL;
		last = NULL;
		//后半段反转
		slow=reverseList(slow);
		fast = head;
		ListNode* temp = NULL;
		while (fast){
			temp = slow;
			slow = slow->next;
			temp->next = fast->next;
			fast->next = temp;
			last = fast->next;
			fast = fast->next->next;
		}
		if (slow)
			last->next = slow;
	}
	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 lst;
	head = lst.createList(head);
	lst.printNode(head);

	lst.reorderList(head);
	lst.printNode(head);

	system("pause");
	return 0;
}