Lintcode 链表插入排序

Given 1->3->2->0->null, return 0->1->2->3->null

/**

• Definition of ListNode
• class ListNode {
• public:
• int val;
• ListNode *next;
• ListNode(int val) {
• this->val = val;
• this->next = NULL;
• }
• } */

class Solution {
public:
/*
* @param head: The first node of linked list.
* @return: The head of linked list.
/
ListNode * insertionSortList(ListNode * head) {
// write your code here
ListNode temp1=head;
if(temp1->next==NULL)
return head;

    vector<int> vec;
    while(temp1!=NULL)
    {
        vec.push_back(temp1->val);
        temp1=temp1->next;
    }
    sort(vec.begin(),vec.end());

    ListNode* returnhead;
    ListNode* temp2=returnhead;
    for (auto c:vec)
    {
        temp2 = new ListNode(c);
        temp2=temp2->next;
    }
    return returnhead;
}

};
请问哪里出错了？