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!!
1 #include "stdafx.h" 2 #include <limits> 3 using namespace std; 4 5 struct ListNode 6 { 7 int val; 8 ListNode *next; 9 ListNode(int x):val(x),next(NULL){} 10 }; 11 class Solution 12 { 13 public: 14 ListNode* insertionSortList(ListNode *head) 15 {//单链表排序：使用插入排序 16 if(head == NULL || head->next == NULL) 17 return head; 18 19 ListNode help(numeric_limits<int>::min());//创建头结点！！！ 20 help.next = head;//!!! 21 22 ListNode *current;//记录当前要排序的节点 23 current = head->next; 24 head->next = NULL; 25 26 ListNode *tmp, *p; 27 while(current) 28 { 29 //从头到尾依次遍历以插入数据 30 //tmp = help.next; 31 tmp = &help; 32 while(tmp && (tmp->val < current->val)) 33 { 34 if((tmp->next) && (tmp->next->val < current->val)) 35 tmp = tmp->next; 36 else 37 break;//找到插入位置 38 } 39 40 p = current->next; 41 current->next = tmp->next; 42 tmp->next = current; 43 current = p; 44 } 45 46 return help.next; 47 } 48 };