LEET code -- 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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/** * Definition for singly-linked list. * struct ListNode { * int val; * struct ListNode *next; * }; */ struct ListNode* swapPairs(struct ListNode* head) { if(head==NULL)return NULL; struct ListNode *Current=head, *Next=head->next; while(Next!=NULL&&Current!=NULL){ int temp=Next->val; Next->val=Current->val; Current->val=temp; Current=Next->next; if(Current!=NULL)Next=Current->next; } return head; }