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.
分析:
将两两相邻的节点交换值,题目简单,只需记录前一个节点的值即可
/**
* 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==NULL||head->next==NULL) return head;
ListNode *l=head;
while(l!=NULL&&l->next!=NULL){
int n=l->val;
l->val=l->next->val;
l->next->val=n;
l=l->next->next;
}
return head;
}
};