leetcode-Swap Nodes in Pairs

Difficulty:
Medium

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.

/**
* 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)
return nullptr;
ListNode *front=head;
ListNode *rear=front->next;

while(rear){
swap(front->val,rear->val);
if(!(front=rear->next))
break;
rear=rear->next->next;
}
return head;
}
};