451. Swap Nodes in Pairs
ListNode * swapPairs(ListNode * head) {
// write your code here
//要用dummy, 要打断三个link，也就重建三个link。dummy->1->2->3,变成dummy -> 2->1->3
if(head == NULL || head->next == NULL){
return head;
}
ListNode *dummy = new ListNode(0);
dummy->next = head;
ListNode *pre = dummy;
while(head != NULL && head->next != NULL){
ListNode *temp = head->next->next;
head->next->next = head; //重建第一个link
pre->next = head->next; //重建第二个link
head->next = temp; //重建第三个link
pre = head;//更新，准备下一次的重建
head = temp;
}
return dummy->next;
}
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