單鏈表實現排序算法之插入排序

插入排序的意思是每次從待排序數列中選出一個，插入到已排序的數列中。

/** 這個是一開始的答案，但是案例沒有全部通過，檢查發現是註釋處修改了head指針所致。
* 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 tony(0);
        ListNode* p = NULL, *q = NULL;
        while (head) {
            p = &tony;
            q = p->next;
            while (q && q->val val) {
                p = p->next;
                q = q->next;
            }
            p->next = head;
            p->next->next = q;
            head = head->next;
        }
        return tony.next;
    }
};

正確答案

/**
* 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 tony(0);
        ListNode* p = NULL, *q = NULL, *t = NULL;
        while (head) {
            p = &tony;
            q = p->next;
            t = head;
            head = head->next;
            while (q && q->val val) {
                p = p->next;
                q = q->next;
            }
            t->next = q;
            p->next = t;
        }
        return tony.next;
    }
};