solution.cpp

/**
 * 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) 
            return head;
        
        ListNode* curr = head -> next;
        head -> next = NULL;
        
        while(curr != NULL)
        {
            ListNode* tmpHead = head;
            ListNode* prev = NULL;
            ListNode* next = curr -> next;
            while(tmpHead != NULL && tmpHead -> val <= curr -> val)
            {
                prev = tmpHead;
                tmpHead = tmpHead -> next;
            }
            
            if(prev != NULL)
            {
                //insert
                if(prev -> next)
                {
                    curr -> next = prev -> next;
                    prev -> next = curr;
                }
                else
                {
                    prev -> next = curr;
                    curr -> next = NULL;
                }
            }
            else
            {
                curr -> next = head;
                head = curr;
            }
            curr = next;
        }
        return head;
    }
};