插入排序进行链表排序

/** * 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 || !head->next) return head;         ListNode dummyHead(0), *p;         dummyHead.next = insertionSortList(head->next);         p = &dummyHead;         while (p && p->next && head->val > p->next->val){             p = p->next;         }         head->next = p->next;         p->next = head;         return dummyHead.next;     } };