24.兩兩交換連結串列中的節點

/**
 * 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 *left, *right, *temp,*end;
        if(head == NULL || head->next == NULL)
        {
            return head;
        }
        left = head;
        right = head->next;
        head = right;
        end = NULL;
        
 
while(left!=NULL&&right!=NULL)
        {
            temp = right->next;
            if(end)
                end->next = right;
            end = left;
            right->next = left;
            left->next = temp;
            left = temp;
            if(left)
            right = left->next;
        }
        
 
return head;
        
    }
};