[LeetCode]Swap Nodes in Pairs

题目描述：（链接）

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.

 

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解题思路：

class Solution {
public:
    ListNode *swapPairs(ListNode *head) {
        if (!head || !(head->next)) {
            return head;
        }
        
        ListNode dummy(-1);
        dummy.next = head;
        ListNode *prev = &dummy;
        ListNode *cur = prev->next;
        ListNode *next = cur->next;
        
        while (next != nullptr) {
            prev->next = next;
            cur->next = next->next;
            next->next = cur;
            
            prev = cur;
            cur = cur->next;
            next = cur? cur->next : nullptr;
        }
        return dummy.next;
    }
};