024 - Swap Nodes in Pairs

Swap Nodes in Pairs

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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Linked List
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(H) Reverse Nodes in k-Group

但就这个in pairs翻转而言，很简单，
但这里的算法并不通用，对于后面提到的 翻转K个，可能要麻烦点，还没多想。

/**
* 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) {
        ListNode dummy(0);
        dummy.next = head;
        if(head && head->next)
        {
            ListNode* oddd = head;
            ListNode* even = head->next;
            ListNode* prev = &dummy;
            while(oddd && even)
            {
                oddd->next = even->next;
                even->next = oddd;
                prev->next = even;
               
                prev = oddd;
                oddd = oddd->next;
                even = (NULL == oddd) ? NULL : oddd->next;
            }
        }
        return dummy.next;
    }
};
4 ms.