LeetCode-M-Insertion Sort List

题意

Sort a linked list using insertion sort.

解法

链表插入算法实现，记录已排好序段的表头和表尾，记录小于当前值的最大节点，注意三种情况：

• 链表头插入
• 链表尾插入
• 链表中插入

实现

/** * 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* tail = head;        ListNode* next = head->next;        while(next != NULL){            ListNode* pre = NULL;            ListNode* cur = head;             while(cur != next && cur->val < next->val){                pre = cur;                cur = cur->next;            }            if(cur == next) {                tail = next;            }else if(pre == NULL){                tail->next = next->next;                next->next = head;                head = next;            }else{                tail->next = next->next;                next->next = pre->next;                pre->next = next;            }            next = tail->next;        }        return head;    }};