链表成对交换问题

要求

给定一个链表1->2->3->4,你会返回2->1->4->3

代码实现

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#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;
        }else{
            ListNode* newHead = new ListNode(0);
            ListNode* pre = head;
            ListNode* p = pre->next;
            ListNode* next = NULL;
            ListNode* nh = newHead;
            while (p!=NULL) {
                next = p->next;
                p->next = pre;
                pre->next = next;
                nh->next = p;
                nh = pre;
                if (next==NULL) {
                    break;
                }
                pre = next;
                p = pre->next;

            }
            return newHead->next;
        }
    }
};
int main(int argc, const char * argv[]) {
    // insert code here...
    std::cout << "Hello, World!\n";
    return 0;
}

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