题目:
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.
解题思路:本题较简单,做3次指针变换就可以完成一轮交换。
代码:
/** * 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 *Zero; ListNode *First=head,*Second; ListNode Forehead(0); if(head==NULL||head->next==NULL)return head; Zero=&Forehead; while(First!=NULL){ Second=First->next; if(Second!=NULL){ First->next=Second->next; Second->next=First; Zero->next=Second; Zero=First; First=First->next; }else{ break; } } return Forehead.next; } };