LeetCode OJ：Insertion Sort List （插入排序链表）

Sort a linked list using insertion sort.

用插入排序来排序一个list，额， 我写的好麻烦啊， debug了好久，至少提交了5次。。。写吐了快，先贴代码，写的也好乱啊：

class Solution {
public:
    ListNode* insertionSortList(ListNode* hed) {
        if (hed == NULL) return NULL;
        head = hed;
        ListNode * insertPosPrev;
        ListNode * afterP;
        ListNode * prev = head;
        ListNode * p = head->next;
        while (p != NULL) {
            if (p->val > prev->val){
                prev = p;
                p = p->next;
                continue;
            }
            insertPosPrev = findInsertPos(p);
            if (insertPosPrev == NULL) {//插入头节点之前
                afterP = p->next;
                prev->next = afterP;
                p->next = head;
                head = p;
                p = afterP;
                continue;
            }
            else if (p != insertPosPrev->next) {
                afterP = p->next;
                prev->next = afterP;
                p->next = insertPosPrev->next;
                insertPosPrev->next = p;
                p = afterP;
                continue;
            }
            prev = p;
            p = p->next;
        }
        return head;
    }

private:
    ListNode * head;

    ListNode * findInsertPos(ListNode * end)
    {
        if (head->val >= end->val)
            return NULL;    //如果插入点在头节点那么返回NULL
        ListNode * prev = head;
        ListNode * p = prev->next;
        while (p != end) {
            if (prev->val < end->val && p->val >= end->val)
                return prev;
            prev = p;
            p = p->next;
        }
        return prev;
    }
};

这里贴一个大神的代码，有时间来看看，暂时还没看懂啊

class Solution
{
public:
    ListNode *insertionSortList(ListNode *head)
    {
        if(head==NULL || head->next==NULL) return head;
        ListNode *cur=head;
        ListNode *helper=new ListNode(0);
        ListNode *pre;
        while(cur)
        {
            ListNode *next=cur->next;
            pre=helper;
            while(pre->next!=NULL && pre->next->val<cur->val)
            {
                pre=pre->next;
            }
            cur->next=pre->next;
            pre->next=cur;
            cur=next;
        }
        return helper->next;
    }
 
} ;

 下面是java写的，第一遍写的基本上可以不看了，写的太麻烦了，下面这个写的稍微简单一点，代码如下：

public class Solution {
    public ListNode insertionSortList(ListNode head) {
        if(head == null) return null;
        ListNode helper = new ListNode(Integer.MIN_VALUE);//将第一个节点的值设置成最小的
        helper.next = head;
        ListNode p = head.next;
        ListNode pPre = head;
        ListNode scan = helper;
        while(p != null){
            if(p.val >= pPre.val){
                p= p.next;
                pPre = pPre.next;
            }else{
                while(p.val > scan.next.val){
                    scan = scan.next;
                }
                if(p.val >= scan.val && p.val <= scan.next.val){
                    ListNode tmp = scan.next;
                    scan.next = p;
                    pPre.next = p.next;
                    p.next = tmp;
                    p = pPre.next;
                    scan = helper; // 将扫描节点重新放置到链表的前部
                }
            }
        }
        return helper.next;
    }
}