[leetcode 24]Swap Nodes in Pairs

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本文介绍了一种链表相邻节点交换算法，该算法仅使用常量空间，并且不修改节点值，只改变节点间的连接关系。通过示例演示了如何实现链表中每两个相邻节点的交换操作。

Given a linked list, swap every two adjacent nodes and return its head.

For example,
Given 1->2->3->4, you should return the list as 2->1->4->3.

Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *swapPairs(ListNode *head) {
        if (!head || !head->next) {
            return head;
        }
        ListNode dummy(-1);
        dummy.next = head;
        auto prev = &dummy;
        auto cur = head;
        auto next = cur->next;
        for (auto prev = &dummy, cur = head, next = cur->next;next; prev = cur, cur = cur->next, next = cur?cur->next:NULL) {
            cur->next = next->next;
            next->next = prev->next;
            prev->next = next;
        }
        return dummy.next;
    }
};