思路

插入排序，維持兩個連結串列，第一個原始連結串列，第二個排好序的連結串列。為了操作方便，第二個連結串列設定一個啞元dummy。當原始連結串列為空或者只有一個元素時，直接返回。如果不是，初始化dummy連結串列。每次從第一個連結串列中拿出一個元素來排序

程式碼

/**
 * 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* dummy = new ListNode(0);
        ListNode* cur = head->next;
        dummy->next = head;
        head->next = NULL;
        
        while
 
(cur != NULL)
        {
            ListNode* next = cur->next;
            ListNode* pos = dummy;
            ListNode* stoppos = dummy->next;
            
            while(stoppos != NULL && cur->val > stoppos->val)
            {
                pos = stoppos;
                stoppos =
 
 stoppos->next;
            }
            
            pos->next = cur;
            cur->next = stoppos;
            cur = next;
        }
        
        return dummy->next;
        
    }
};