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24.cpp
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27 lines (27 loc) · 710 Bytes
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/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution {
public:
ListNode* swapPairs(ListNode* head) {
if(!head || !head->next) return head;
ListNode *one=head,*two=head->next,*prev=NULL;
head=head->next;
while(one && two){
one->next=two->next;
two->next=one;
if(prev) prev->next=two;
prev=one;
one=one->next;
if(one) two=one->next;
}
return head;
}
};