[leetcode] Insertion Sort List

Insertion Sort List

#include "iostream"
using namespace std;

/**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||head->next==NULL) {
            return head;
        }
        
        ListNode *p=head->next;//待排序
        ListNode *res =new ListNode(0);//已排序
        res->next=head;
        head->next=NULL;
        
        ListNode *preq=res;
        ListNode *q=preq->next;
        
        while (p!=NULL) {
            
            while (q!=NULL&&p->val>q->val) {
                preq=q;
                q=q->next;
            }
            
            preq->next=p;
            p=p->next;
            preq=preq->next;
            preq->next=q;
            
            preq=res;
            q=preq->next;
        }
        
        res->next=NULL;
        delete res;
        return q;
    }
};


int main() {
    ListNode *t=new ListNode(3);
    t->next=new ListNode(2);
    t->next->next=new ListNode(1);
    cout<<t->val<<endl;
    Solution so;
    ListNode *res= so.insertionSortList(t);
    cout<<res->val<<res->next->val<<endl;
    return 0;
}