leetcode Question: Insertion Sort List

Insertion Sort List

Sort a linked list using insertion sort.

Analysis:

The insertion sorting on array can be found in my previous post (here).
The general idea is insert the current element A[i] into the proper position from A[0]...A[i-1], and A[0]...A[i-1] is already sorted.

In this problem, we can use the same idea and linked list provides a more efficient way for insertion.  Details can be found in the code below. Note that after the insertion, the position of P is unchanged but should not provide another p=p->next operation.

Code:

/**
 * 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){return NULL;}
        ListNode *p=new ListNode(0);
        p->next = head;
        head = p;
        ListNode *q;
        
        while (p->next!=NULL){
            q = head;
            bool flag = false;
            while (q!=p){
                if (q->next->val>p->next->val){
                    ListNode* tmp1=p->next;
                    p->next =p->next->next;
                    tmp1->next = q->next;
                    q->next = tmp1;
                    flag =true;
                    break;
                }else{
                    q=q->next;    
                }
            }
            if (!flag){
                p=p->next;
            }
        }
        return head->next;
    }
};