leetcode Insertion Sort List

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *insertionSortList(ListNode *head) {
if(head == NULL){
return head;
}
ListNode* tmp = head;
int len  = 1;
while(tmp->next){
tmp = tmp->next;
len++;
}
ListNode* rec = head->next;
ListNode* prev;
ListNode dummy(-1);
dummy.next = head;
ListNode* prevrec = head;
for(int i = 1; i < len; ++i){
tmp = rec;
ListNode* iter = dummy.next;
prev = &dummy;
bool insert = false;
while(iter != tmp){
if(iter->val > tmp->val){
if(iter->next == tmp){
int swint = tmp->val;
tmp->val = iter->val;
iter->val = swint;
rec = tmp->next;
prevrec = tmp;
}
else{
//insert tmp between prev and iter
//prevrec remains unchanged
rec = tmp->next;
prev->next = tmp;
tmp->next = iter;
prevrec->next = rec;
}
insert = true;
break;
}
else{
prev = iter;
iter = iter->next;
}
}
if(!insert){
rec = tmp->next;
prevrec = tmp;
}

}
return dummy.next;
}
};