No.147 Insertion Sorted List

No.147 Insertion Sorted List

Sort a linked list using insertion sort.

单链表排序：使用插入排序

时间复杂度是排序算法的O(n^2)，空间复杂度是O(1)

难度：无他，把思路理顺，注意细节，并测试一下；另外头结点的巧妙应用，int最小表示方式!!

#include "stdafx.h"
#include <limits>
using namespace std;

struct ListNode
{
    int val;
    ListNode *next;
    ListNode(int x):val(x),next(NULL){}
};
class Solution
{
public:
    ListNode* insertionSortList(ListNode *head)
    {//单链表排序：使用插入排序
        if(head == NULL || head->next == NULL)
            return head;

        ListNode help(numeric_limits<int>::min());//创建头结点！！！
        help.next = head;//!!!

        ListNode *current;//记录当前要排序的节点
        current = head->next;
        head->next = NULL;

        ListNode *tmp, *p;
        while(current)
        {
            //从头到尾依次遍历以插入数据
            //tmp = help.next;
            tmp = &help;
            while(tmp && (tmp->val < current->val))
            {
                if((tmp->next) && (tmp->next->val < current->val))
                    tmp = tmp->next;
                else
                    break;//找到插入位置
            }
            
            p = current->next;
            current->next = tmp->next;
            tmp->next = current;
            current = p;
        }

        return help.next;
    }
};