I don't know where is wrong

  • 0

    when input is [1,2] , this will be TLE.

    struct ListNode* swapPairs(struct ListNode* head) {

    struct ListNode* newhead = malloc(sizeof(struct ListNode));
    struct ListNode* tmp;
    struct ListNode* a;
    a = newhead;
    while(head !=NULL && head->next!=NULL)   
        tmp= head->next->next;
        newhead->next = head->next;
        newhead->next->next = head;
        newhead = newhead->next->next;
    if(head !=NULL)
        newhead->next = head;
    return a->next;


  • 0

    That's because the linked list becomes a loop. You need to make head->next point to tmp before head points to tmp.

  • 0

    Hi guys, I encountered the same problem. I have looked at @triple's suggestion, but I couldn't understand. Could any of you explain more? or show me how to solve the cycle? Thanks.

  • 0

    @triple was right, after that becomes [2,1]. Since [1] still points to [2], which means [1]->next is equal to [2]. I think the test needs to move on to the next ListNode, but for your code this will never succeed because [1]->next is always [2] so you got the TLE.

  • 0

    @yizhu59 you have to make the final ListNode points to NULL instead of other ListNode.

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