147. Insertion Sort List

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode* insertionSortList(ListNode* head) {
12         if (head == nullptr) return nullptr;
13         else {
14             ListNode dummy(INT_MIN);  // 这里需要考虑如果数组中含有INT_MIN的情况
15             dummy.next = head;
16             ListNode* prev = head;
17             ListNode* curr = head->next;
18             while (curr != nullptr) {
19                 ListNode* ptr = &dummy;
20                 if (curr->val < prev->val) {
21                     ListNode* tmp = curr->next;
22                     ListNode* beforePtr = nullptr;
23                     while (ptr->val <= curr->val) {  // 这里需要有等号，处理数组中含有INT_MIN的情况
24                         beforePtr = ptr;
25                         ptr = ptr->next;
26                     }
27                     beforePtr->next = curr;   // 注意指针的修改
28                     curr->next = ptr;
29                     curr = tmp;
30                 } else {
31                     prev->next = curr;      // 注意指针的修改
32                     prev = prev->next;
33                     curr = curr->next;
34                 }
35             }
36             prev->next = curr;
37             return dummy.next;
38         }
39     }
40 };