【leetcode】【单链表】【24】Swap Nodes in Pairs

#include<iostream>
using namespace std;

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

class Solution {
public:
	ListNode* swapPairs(ListNode* head) {
		if (head==NULL || head->next==NULL)
			return head;
		
		ListNode* first = head;
		ListNode* second = first->next;
		first->next = second->next;
		second->next = first;
		head = second;
		ListNode* preFirst = first;
		first = first->next;
		if (first) //注意
			second = first->next;
		while (first&&second){
			first->next = second->next;
			second->next = first;
			preFirst->next = second;

			preFirst = first;
			first = first->next;
			if (first)//注意
				second = first->next;
		}
		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(){
	Solution solution;

	ListNode* head = NULL;
	head = solution.createList(head);
	solution.printNode(head);

	head = solution.swapPairs(head);
	solution.printNode(head);
	system("pause");
	return 0;
}