LeetCode-Insertion Sort List

Sort a linked list using insertion sort.

/**
 * 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) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(head==NULL)return NULL;
        if(head->next==NULL)return head;
        ListNode* ret=head;
        ListNode* ptr,*tmp;
        head=head->next;
        ret->next=NULL;//Don't forget this one!
        while(head!=NULL){
            if(head->val<ret->val){
                ptr=head->next;
                head->next=ret;
                ret=head;
                head=ptr;
            }
            else{
                ptr=ret;
                while(ptr->next!=NULL&&ptr->next->val<head->val){
                    ptr=ptr->next;
                }
                tmp=head->next;
                head->next=ptr->next;
                ptr->next=head;
                head=tmp;
            }
        }
        return ret;
    }
};