[Leetcode] Insertion Sort List

Sort a linked list using insertion sort.

虽然算法很简单，但是链表操作起来实正是烦啊，特别要注意各种边界条件。

/**
 * 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 *h = new ListNode(0);
    h->next = head;
    ListNode *p, *q, *tmp;
    bool flag;
    for (p = head; p->next != NULL;) {
        flag = false;
        for (q = h; q != p; q = q->next) {
            if (p->next->val < q->next->val) {
                tmp = p->next;
                p->next = tmp->next;
                tmp->next = q->next;
                q->next = tmp;
                flag = true; break;
            }
        }
        if (!flag) p = p->next;
    }
    head = h->next;
    delete h; h = NULL;
    return head;
    }
};